ITEM 1A. RISK FACTORS

Investing in our securities involves a high degree of risk. You should consider carefully the following information about the risks described below, together with the other information contained in this Report and in our other public filings in evaluating our business. If any of the following risks actually occur, our business could be materially harmed, and our financial condition and results of operations could be materially and adversely affected. As a result, the trading price of our securities could decline, and you might lose all or part of your investment. The risks and uncertainties described below are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently believe to be immaterial may also adversely affect our business.

Risks Related to Our Financial Condition and Need for Additional Capital

We have a limited operating history and may never become profitable.

Ionis Pharmaceuticals, Inc., or Ionis, incorporated us as a Delaware corporation in December 2014, and we have operated as an affiliate of Ionis since that time. As such, we have limited experience as a company, and no experience operating independently from Ionis, and have not yet demonstrated that we can successfully overcome many of the risks and uncertainties frequently encountered in new and rapidly evolving fields, particularly the biotechnology and pharmaceutical fields.

As a company, we have limited experience commercializing products. Our ability to generate substantial revenue and achieve profitability depends on our ability, alone or with strategic partners, to successfully develop our drugs, obtain the regulatory approvals necessary to commercialize our drugs, including WAYLIVRA ^TM (volanesorsen), AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, and continue the commercialization of TEGSEDI ^TM (inotersen). Although we received our first revenue from product sales in the fourth quarter of 2018, if we are not successful in growing revenue and controlling costs, we will not achieve profitable operations or positive cash flow, and even if we achieve profitability in the future, we may not sustain profitability in subsequent periods. Our ability to generate revenue sufficient to achieve profitability from product sales depends heavily on our and our current and future strategic partners' success in:

30

We may not successfully develop our products or generate product revenue sufficient to cover operating expenses or become profitable. If we cannot achieve or maintain profitability, it would depress the market price of our common stock and could impair our ability to raise capital, expand our business, diversify our product offerings or continue our operations. If the market price of our common stock declined, you could lose all or part of your investment.

We have incurred losses since our inception.

Because drug development requires substantial lead-time and funding prior to commercialization, we have incurred expenses while generating limited revenue from our operating activities since our formation. Our net losses were $225.8 million and $121.6 million for the years ended December 31, 2018 and December 31, 2017 (as revised), respectively. As of December 31, 2018, we had an accumulated deficit of approximately $522.0 million. Most of the losses resulted from costs incurred in connection with our development programs and from general and administrative costs associated with our operations. We expect to incur additional operating losses for the foreseeable future, and these losses may increase if we cannot generate substantial revenue.

We will require substantial additional funding to achieve our goals. If we fail to obtain timely funding, we may need to curtail or abandon some of our programs.

All of our drugs are undergoing clinical studies. All of our drug programs, except TEGSEDI in the United States, EU, and Canada, will require additional nonclinical and/or clinical testing and/or marketing authorization prior to commercialization. We will need to spend significant additional resources to conduct these activities. Our expenses could increase beyond expectations if the U.S. Food and Drug Administration, or FDA, the European Medicines Agency, or EMA, or other regulatory authorities require us to perform clinical studies and other studies in addition to those that we currently anticipate. As of December 31, 2018, we had cash, cash equivalents and investments equal to $252.6 million. Our operating expenses were $295.7 million and $163.9 million for the ended December 31, 2018 and December 31, 2017, respectively.

Prior to our IPO, we funded our operating activities through a $100.0 million cash contribution we received from Ionis in 2015, $75.0 million that we received from initiating our collaboration with Novartis and $106.0 million in drawdowns under our line of credit with Ionis. The line of credit converted to our common stock when we closed our IPO. We no longer have access to the line of credit following the closing of our IPO and we do not have any firm commitment from Ionis to fund our cash flow deficits or provide other direct or indirect financial assistance to us. Additionally, in July 2017 we received $182.3 million in net proceeds from our IPO including $25.0 million that Ionis invested in our IPO and the Novartis concurrent private placement of $50.0 million. In April 2018, we received $200.0 million from the common stock we issued in connection with the licensing transaction with Ionis discussed in Note 7, License Agreements and Services Agreement with Ionis , to our consolidated financial statements included in this Form 10-K. We expect that we will need to raise additional funding to continue developing the drugs in our pipeline and to seek regulatory approval for and to commercialize TEGSEDI, WAYLIVRA and other drugs in our pipeline.

We have received marketing authorization approval for TEGSEDI from the FDA for the treatment of the polyneuropathy of hATTR in adult patients in the United States, from the European Commission, or EC, and from Health Canada for the treatment of stage 1 or stage 2 polyneuropathy in adult patients with hATTR, and we will continue to incur significant costs commercializing TEGSEDI. Even if we obtain marketing authorizations to sell WAYLIVRA, AKCEA-APO(a)-L _Rx or AKCEA-TTR-L _Rx , we will incur

31

significant costs to commercialize the approved product. To date, only one of our product ( s ) , TEGSEDI, has commercially launched, and even if we generate substantial revenue from the sale of approved products, we may not become profitable and would need to obtain additional funding to continue operations.

Risks Related to Clinical Development, Regulatory Review and Approval of Our Drugs

If the results of clinical testing indicate that any of our drugs are not suitable for commercial use, we may need to abandon one or more of our drug development programs.

Drug discovery and development has inherent risks and the historical failure rate for drugs is high. Antisense drugs are a relatively new approach to therapeutics. If we cannot demonstrate that our drugs are safe and effective for human use in the intended indication, we may need to abandon one or more of our drug development programs.

If any of our drugs in clinical studies, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, do not show sufficient safety and efficacy in patients with the targeted indication, it would negatively affect our development and commercialization goals for the drug and we would have expended significant resources with little or no benefit to us.

Even if our drugs are successful in preclinical and earlier-stage clinical studies, the drugs may not be successful in later-stage clinical studies.

Successful results in preclinical or initial clinical studies, including the results of earlier studies for our drugs in development, may not predict the results of subsequent clinical studies, including the Phase 3 study of WAYLIVRA for the treatment of FPL and the Phase 3 study of AKCEA-APO(a)-L _Rx in patients with established cardiovascular disease and elevated levels of lipoprotein(a). There are a number of factors that could cause a clinical study to fail or be delayed, including:

In addition, WAYLIVRA and AKCEA-APOCIII-L _Rx have the same mechanism of action, TEGSEDI and AKCEA-TTR-L _Rx , also have the same mechanism of action and all of our current drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx , AKCEA-ANGPTL3-L _Rx and AKCEA-APOCIII-L _Rx , are chemically similar to each other and the drugs Ionis and other companies are developing separately. As a result, a safety observation we, Ionis or other companies encounter with one of our or their drugs could have or be perceived by a regulatory authority to have an impact on a different drug we are developing. This could cause the FDA and other regulators to ask questions or take actions that could harm or delay our ability to develop and commercialize our drugs or

32

increase our costs. For example, the FDA or other regulatory agencies could request, among other things, any of the following regarding one of our drugs: additional information or commitments before we can start or continue a clinical study, protocol amendments, increased safety monitoring, additional product labeling information, and post-approval commitments. Similarly, we have an ongoing Phase 3 study of WAYLIVRA in patients with FPL, an ongoing open label extension study of WAYLIVRA in patients with FCS and an open label extension study of TEGSEDI in patients with hATTR, and an early access program, or EAP, for both WAYLIVRA and TEGSEDI. Adverse events or results from these studies or the EAPs could negatively impact our pending or future marketing approval applications for WAYLIVRA and TEGSEDI in patients with FCS or hATTR amyloidosis or the commercial opportunity for WAYLIVRA or TEGSEDI. In August 2018 we received a Complete Response Letter, or CRL , from the FDA regarding the new drug application for WAYLIVRA in which the FDA determined that the safety concerns identified with WAYLIVRA in our clinical development program outweighed the expected benefits of triglyceride lowering in patients with FCS. We also received a Notice of Noncompliance withdrawal letter, or Non-W, from Health Canada for WAYLIVRA in November 2018. We and Ionis are engaged with the FDA and plan to work with Health Canada to confirm a path forward for WAYLIVRA. As a result, we will need to submit additional data to FDA and may need to conduct additional clinical studies before obtaining marketing authorization, which in turn could delay or prevent us from generating any revenue or profit from the sale of WAYLIVRA. The regulatory authorities and Europe could have a similar response to the pending marketing authorization application. Any failure or delay in the clinical studies for any of our drugs in development could reduce the commercial potential or viability of our drugs.

We may not have appropriately designed the planned and ongoing clinical studies for WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development to support submission of a marketing application to the FDA and foreign regulatory authorities or demonstrate safety or efficacy at the level required by the FDA and foreign regulatory authorities for product approval.

We completed a Phase 3 clinical program for WAYLIVRA for the treatment of FCS in 2018 and are conducting or plan to conduct additional clinical studies for WAYLIVRA in patients with FPL, as well as for AKCEA-TTR-L _Rx, AKCEA-APO(a)-L _Rx , AKCEA-ANGPTL3-L _Rx and AKCEA-APOCIII-L _Rx .

Even if we achieve positive results on the endpoints for these clinical studies or any future clinical studies, the FDA or foreign regulatory authorities may believe the clinical studies do not show the appropriate balance of safety and efficacy in the indication being sought or may interpret the data differently than we do, and deem the results insufficient to demonstrate the appropriate balance of safety and efficacy at the level required for product approval. For example, in August 2018 we received a CRL from the FDA regarding the new drug application for WAYLIVRA in which the FDA determined that the safety concerns identified with WAYLIVRA in our clinical development program outweighed the expected benefits of triglyceride lowering in patients with FCS. We also received a Non-W from Health Canada for WAYLIVRA in November 2018. We and Ionis are engaged with the FDA and plan to work with Health Canada to confirm a path forward for WAYLIVRA. As a result, we will need to submit additional data to the FDA and may need to conduct additional clinical studies before obtaining marketing authorization, which in turn could delay or prevent us from generating any revenue or profit from the sale of WAYLIVRA. The CHMP of the EMA has adopted a positive opinion recommending conditional marketing authorization of WAYLIVRA as an adjunct to diet in adult patients with genetically confirmed FCS who are at high risk for pancreatitis, in whom response to diet and triglyceride lowering therapy has been inadequate. The positive opinion will now be referred to the EC, which grants marketing authorization for medicines in the European Union, as well as to European Economic Area members Iceland, Liechtenstein and Norway, however, the EC may decide not to adopt the CHMP’s positive opinion . These risks are more likely to occur since we are developing our drugs against therapeutic targets or to treat diseases in which there is little or no clinical experience. In addition, these risks may be more likely to occur for WAYLIVRA since there were some patients in the Phase 3 program that experienced serious platelet events (grade 4 thrombocytopenia), a condition in which the patient has very low platelet levels, and additional patients experienced other adverse events in the program, including patients who discontinued participation in the APPROACH study due to platelet count declines. We believe that the enhanced monitoring we have implemented to support early detection and management of these issues can help manage these safety issues so that patients can continue treatment. Since implementation of the enhanced monitoring, serious platelet events have been infrequent.

We may make modifications to the clinical study protocols or designs of our ongoing clinical studies that delay enrollment or completion of such clinical studies and could delay regulatory approval of WAYLIVRA and our other drugs in development. Any failure to obtain approval for WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development on the timeline that we currently anticipate, or at all, would have a material and adverse impact on our business, prospects, financial condition and results of operations and could cause our stock price to decline.

33

Clinical studies for WAYLIVRA, AKCEA-APO(a)-L _Rx , AKCEA-TTR-L _Rx , AKCEA-ANGPTL3-L _Rx , AKCEA-APOCIII-L _Rx or our other drugs may not demonstrate safety or efficacy at the level required by the FDA and foreign regulatory authorities for product approval.

The EMA is currently reviewing our application for regulatory approval for WAYLIVRA. The CHMP of the EMA has adopted a positive opinion recommending conditional marketing authorization of WAYLIVRA as an adjunct to diet in adult patients with genetically confirmed FCS who are at high risk for pancreatitis, in whom response to diet and triglyceride lowering therapy has been inadequate. The positive opinion will now be referred to the EC, which grants marketing authorization for medicines in the European Union, as well as to European Economic Area members Iceland, Liechtenstein and Norway, however, the EC may decide not to adopt the CHMP’s positive opinion . We and Ionis are conducting or intend to conduct clinical studies for AKCEA-APO(a)-L _Rx , AKCEA-TTR-L _Rx , AKCEA-ANGPTL3-L _Rx and AKCEA-APOCIII-L _Rx.

Even if positive results on the endpoints for the clinical studies are achieved, the FDA or foreign regulatory authorities may believe the clinical studies do not show the appropriate balance of safety and efficacy in the indication being sought or may interpret the data differently than we do, and may deem the results insufficient to demonstrate the appropriate balance of safety and efficacy at the level required for product approval. For example, in August 2018 we received a CRL from the FDA regarding the new drug application for WAYLIVRA in which the FDA determined that the safety concerns identified with WAYLIVRA in our clinical development program outweighed the expected benefits of triglyceride lowering in patients with FCS. We also received a Non-W from Health Canada for WAYLIVRA in November 2018. We and Ionis are engaged with the FDA and plan to work with Health Canada to confirm a path forward for WAYLIVRA. As a result, we will need to submit additional data to FDA and may need to conduct additional clinical studies before obtaining marketing authorization, which in turn could delay or prevent us from generating any revenue or profit from the sale of WAYLIVRA. The regulatory authorities in Europe could have a similar response to the pending marketing authorization application. As an additional example, the foreign regulatory authorities could claim that we have not tested WAYLIVRA, AKCEA-APO(a)-L _Rx , AKCEA-TTR-L _Rx , AKCEA-ANGPTL3-L _Rx and AKCEA-APOCIII-L _Rx in a sufficient number of patients to demonstrate that the drug is safe and effective in patients with other indications to support an application for marketing authorization for the applicable indication. In such a case, we may need to conduct additional clinical studies before obtaining marketing authorization, which would be expensive and delay the development and commercialization of the drug.

Any failure to obtain approvals for WAYLIVRA in other important markets outside of the United States and Canada, including the EU, on the timeline that we currently anticipate, or at all, would have a material and adverse impact on our business, prospects, financial condition and results of operations and could cause our stock price to decline.

If we or our partners fail to obtain regulatory approval for our drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, or additional approvals for TEGSEDI, we or our partners cannot sell them in the applicable markets.

We cannot guarantee that any of our drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, will be safe and effective, or will be approved or receive additional approvals for commercialization. We and our partners must conduct time-consuming, extensive and costly clinical studies to demonstrate the safety and efficacy of each of our drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, before they can be approved, or receive additional approvals, for sale. We and our partners must conduct these studies in compliance with FDA regulations and with comparable regulations in other countries.

We or our partners may not obtain necessary regulatory approvals on a timely basis, if at all, for any of our drugs. It is possible that regulatory authorities will not approve TEGSEDI in additional markets or any of our other drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, for marketing. If the FDA or another regulatory authority believes that we or our partners have not sufficiently demonstrated the safety or efficacy of any of our drugs, including WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, the authority will not approve the specific drug or will require additional studies, which can be time consuming and expensive and which will delay or harm our ability to successfully commercialize the drug. For example, in August 2018 we received a CRL from the FDA regarding the new drug application for WAYLIVRA in which the FDA determined that the safety concerns identified with WAYLIVRA in our clinical development program outweighed the expected benefits of triglyceride lowering in patients with FCS. We also received a Non-W from Health Canada for WAYLIVRA in November 2018. We and Ionis are engaged with the FDA and plan to work with Health Canada to confirm a path forward for WAYLIVRA. As a result, we will need to submit additional data to FDA and may need to conduct additional clinical studies before obtaining marketing authorization, which in turn could delay or prevent us from generating any revenue or profit from the sale of WAYLIVRA. The regulatory authority in Europe could have a similar response to the pending marketing authorization.

34

The FDA or other comparable foreign regulatory authorities can delay, limit or deny approval of a drug for many reasons, including:

Failure to successfully develop WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, or to receive marketing authorization for these drugs in important markets or delays in these authorizations would prevent or delay the commercial launch of the drug, and, as a result, would negatively affect our ability to generate revenue.

We may not be able to benefit from orphan drug designation for WAYLIVRA, TEGSEDI or any of our other drugs.

The FDA and EMA have granted orphan drug designation to TEGSEDI and to WAYLIVRA for the treatment of patients with FCS. In addition, the EMA has granted orphan drug designation to WAYLIVRA for the treatment of patients with FPL. The FDA, however, refused to grant our request for orphan drug designation for WAYLIVRA for the treatment of patients with FPL in the United States in 2017.

In the United States, under the Orphan Drug Act, the FDA may designate a drug as an orphan drug if it is intended to treat a rare disease or condition, which is generally defined as a patient population of fewer than 200,000 individuals in the United States. Orphan drug designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process, but it can provide financial incentives, such as tax advantages and user-fee waivers, as well as longer regulatory exclusivity periods.

Even if approval is obtained on a drug that has been designated as an orphan drug, we may lose orphan drug exclusivity if the FDA determines that the request for designation was materially defective or if we cannot assure sufficient quantity of the applicable drug to meet the needs of patients with the rare disease or condition, or if a competitor is able to gain approval for the same drug in a safer or more effective form or that makes a major contribution to patient care.

Even if we maintain orphan drug exclusivity for TEGSEDI or WAYLIVRA for the treatment of patients with FCS or obtain orphan drug exclusivity for our other drugs, the exclusivity may not effectively protect the drug from competition because regulatory authorities still may authorize different drugs for the same condition.

We may expend our limited resources to pursue a particular drug or indication and fail to capitalize on drugs or indications that may be more profitable or for which there is a greater likelihood of success.

We will continue to dedicate a substantial amount of our resources to commercialize TEGSEDI and support the continued development of AKCEA-TTR-L _Rx . In addition, we may dedicate a substantial amount of our resources to develop and seek regulatory approval for WAYLIVRA to treat patients with FCS and FPL. As a result, we may forego or delay pursuit of opportunities with our other drugs or for other indications that later prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial drugs or profitable market opportunities. Our spending on current and future research and development programs and drugs for specific indications may not yield any commercially viable drugs.

35

Our drugs, including TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, could be subject to regulatory limitations following approval.

Following approval of a drug, we and our partners must comply with comprehensive government regulations regarding the manufacture, marketing and distribution of drug products. Promotional communications regarding prescription drugs must be consistent with the information in the product's approved labeling. We and our partners may not obtain the labeling claims necessary or desirable to successfully commercialize our drug products, including TEGSEDI, and if approved, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development.

The FDA and foreign regulatory authorities can impose significant restrictions on an approved drug product through the product label and on advertising, promotional and distribution activities. For example:

In addition, when approved, the FDA or a foreign regulatory authority may condition approval on the performance of post-approval clinical studies or patient monitoring, which could be time consuming and expensive. If the results of such post-marketing studies are not satisfactory, the FDA or a foreign regulatory authority may withdraw marketing authorization or may condition continued marketing on commitments from us or our partners that may be expensive and/or time consuming to fulfill.

In addition, if we or others identify side effects after any of our drug products are on the market, if manufacturing problems occur subsequent to regulatory approval, or if we, our manufacturers or our partners fail to comply with regulatory requirements, we or our partners could be subject to:

Any one or a combination of these events could prevent us from achieving or maintaining market acceptance of the affected drug product or could substantially increase the costs and expenses of commercializing such drug product, which in turn could delay or prevent us from generating any revenue or profit from the sale of the drug product.

36

The development and commercialization of TEGSEDI and WAYLIVRA may place strain on our management team’s time and attention and may divert our management team’s attention from our other existing products.

Although we have personnel with experience commercializing drugs, we ourselves have limited experience commercializing products. We commercially launched TEGSEDI during the fourth quarter of 2018 and, if regulatory approval is obtained, we plan to commercially launch WAYLIVRA during 2019. The commercial launch of TEGSEDI will continue to and, if approved, the commercial launch of WAYLIVRA will, require significant efforts and the devotion of substantial resources, as we finalize regulatory submissions, manage the manufacturing of sufficient quantities of product to support long-term commercial sales and integrate, optimize or maintain, as applicable, the global sales, marketing, medical, for each of WAYLIVRA and TEGSEDI, and patient support infrastructure, which may place pressure on the management team ’ s time and attention. These efforts may also divert the attention of the management team from our other business operations, such as the development or commercialization of our other pipeline products, including AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx, AKCEA-ANGPTL3-L _Rx and AKCEA-APOCIII-L _Rx . As a result, our business, results of operations, financial condition and prospects for future growth could be adversely impacted and the market price of our common stock may decline.

Risks Related to Commercialization of Our Drugs

If we cannot effectively manage our marketing and sales capabilities or enter into agreements with third parties to market and sell our drug products, we may not generate product revenue.

We commercially launched TEGSEDI in the fourth quarter of 2018 and, if approved, plan to commercialize WAYLIVRA.  To successfully commercialize TEGSEDI and WAYLIVRA, we must effectively manage our marketing, sales and distribution capabilities or make arrangements with third parties to perform these services. We may not be successful in doing so. To commercialize WAYLIVRA in the initial indications we plan to pursue and to continue the commercialization of TEGSEDI, we will need to optimize and maintain specialty sales forces in the global regions where we currently market or expect to market TEGSEDI and WAYLIVRA, supported by case managers, reimbursement specialists, partnerships with specialty pharmacies, injection training, routine blood and urine monitoring and a medical affairs team. We may seek to further penetrate markets by expanding our sales forces or through strategic partnerships with other pharmaceutical or biotechnology companies or third-party sales organizations.

Even though certain members of our management team and other employees have significant experience commercializing drug products, as a company we have limited experience marketing, selling or distributing drug products, and there are significant risks involved in building and managing a commercial infrastructure. It is expensive and time consuming for us to maintain our own sales forces and related compliance protocols to market TEGSEDI and it will be increasingly expensive and time consuming as we commercially launch additional drug products, if approved. We may never successfully optimize or manage this capability and any failure could delay or preclude the commercial launch of WAYLIVRA or adversely affect TEGSEDI sales. We and our partners, if any, will have to compete with other companies to recruit, hire, train, manage and retain marketing and sales personnel. As a result of our receipt of a CRL from the FDA regarding the new drug application for WAYLIVRA, on September 6, 2018, we enacted a plan to reorganize our workforce to better align with the immediate needs of our business. In connection with this reorganization plan, we reduced our workforce by approximately 12%. If WAYLIVRA is subsequently approved in the United States, we will again need to increase our operations and expand our use of third-party contractors.

We have incurred expenses launching TEGSEDI in the EU, Canada and the U.S. and integrating and managing the marketing and sales infrastructure. If regulatory requirements or other factors cause the commercialization of TEGSEDI to be less successful than expected in important markets, we would incur additional expenses for having invested in these capabilities prior to realizing any significant revenue from sales of TEGSEDI. Our sales force and marketing teams may not successfully commercialize TEGSEDI.

We will incur expenses prior to the launch of WAYLIVRA to integrate and manage the marketing and sales infrastructure. If regulatory requirements or other factors cause a delay in the commercial launch of WAYLIVRA, we would incur additional expenses for having invested in these capabilities earlier than required and prior to realizing any revenue from sales of WAYLIVRA. Our sales force and marketing teams may not successfully commercialize WAYLIVRA.

37

To the extent we decide to rely on third parties to commercialize TEGSEDI or WAYLIVRA in a particular geographic market, we may receive less revenue than if we commercialized TEGSEDI or WAYLIVRA by ourselves. For example, in August 2018, we granted PTC Therapeutics International Limited, or PTC Therapeutics, the exclusive right to commercialize TEGSEDI and WAYLIVRA in Latin America and certain Caribbean countries, and will continue to rely on PTC Therapeutics to commercialize TEGSEDI and WAYLIVRA in those geographic markets. In addition, in August 2018 we entered into an agreement with Accredo Health Group, Inc., or Accredo, a subsidiary of Express Scripts, to be our specialty pharmacy partner for distribution of TEGSEDI in the U.S. Further , we have less control over the sales efforts of other third parties, including PTC Therapeutics and Accredo, involved in commercializing TEGSEDI or WAYLIVRA.

If we cannot effectively build and manage our distribution, medical affairs, market access, marketing and sales infrastructure, or find a suitable third party to perform such functions, the sales of TEGSEDI and commercial launch of WAYLIVRA may be adversely affected, which could have a material adverse effect on our business, prospects, financial condition and results of operations.

If we are unable to rely on third-party specialty channels to distribute our drugs to patients we may be unable to generate adequate revenue

We and our strategic partners have contracted with, rely on and will continue to rely on third-party specialty pharmacies to distribute our drugs to patients. A specialty pharmacy is a pharmacy that specializes in dispensing medications for complex or chronic conditions, a process that requires a high level of patient education and ongoing management. Our management team will need to devote a significant amount of its attention to optimizing and managing this distribution network. If we cannot effectively optimize and manage this distribution process, the commercial launch of WAYLIVRA, AKCEA-APO(a)-L _Rx and AKCEA-TTR-L _Rx and the sales of TEGSEDI will be adversely affected.

In addition, the use of specialty pharmacies involves certain risks, including, but not limited to, risks that these organizations will:

Any such events may result in decreased sales and lower revenue, which could have a material adverse effect on our business, prospects, financial condition and results of operations.

If the market does not accept our drugs, including TEGSEDI, WAYLIVRA, AKCEA-TTR-L _Rx and our other drugs in development, we are not likely to generate substantial product revenue or become profitable.

Even though we have obtained marketing authorization approval from the FDA, the EC and Health Canada for TEGSEDI, and if we or our strategic partners obtain a marketing authorization for WAYLIVRA, AKCEA-TTR-L _Rx and our other drugs in development, our success will depend upon the medical community, patients and third-party payors accepting our drugs as medically useful, cost-effective, safe and convenient. Even if the FDA or foreign regulatory authorities authorize our drugs for commercialization, doctors may not prescribe our drugs to treat patients. We and our partners may not successfully commercialize additional drugs.

Additionally, in many of the markets where we or our partners may sell our drugs in the future, if we cannot agree with the government or other third-party payors regarding the price we can charge for our drugs, then we may not be able to sell our drugs in that market. Similarly, cost control initiatives by governments or third-party payors could decrease the price received for our drugs or increase patient coinsurance to a level that makes the continued commercializing of TEGSEDI and the commercializing of WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development economically unviable.

38

The degree of market acceptance for TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development depends upon a number of factors, including the:

Based on the profile of our drugs, physicians, patients, patient advocates, payors or the medical community in general may not accept and/or use any drugs that we may develop.

For example, the product label for TEGSEDI in the United States has a boxed warning for thrombocytopenia and glomerulonephritis, requires periodic blood and urine monitoring, and TEGSEDI has a Risk Evaluation and Mitigation Strategy, or REMS, program. Our main competition in the U.S. market for TEGSEDI is ONPATTRO (patisiran), marketed by Alnylam Pharmaceuticals, Inc. Although ONPATTRO requires intravenous administration and pre-treatment with steroids, it does not have a boxed warning or REMS. Additionally, in the clinical studies with WAYLIVRA, declines in platelet counts were observed in many patients and some patients discontinued the study because of platelet declines. Therefore, we expect the product label for WAYLIVRA will require periodic blood monitoring. In each case, these label requirements could negatively affect our ability to attract and retain patients for these drugs. We believe that the enhanced monitoring we have implemented to support early detection and management of these issues can help manage these safety issues so that patients can continue treatment. Since implementation of the enhanced monitoring, serious platelet events have been infrequent. While we believe we can better maintain patients on TEGSEDI and WAYLIVRA through our patient-centric commercial approach where we plan to have greater involvement with physicians and patients, if we cannot effectively maintain patients on TEGSEDI and WAYLIVRA, we may not be able to generate substantial revenue from TEGSEDI and WAYLIVRA sales.

The patient populations suffering from FCS and FPL are small and have not been established with precision. If the actual number of patients is smaller than we estimate, or if we cannot raise awareness of these diseases and diagnosis is not improved, our revenue and ability to achieve profitability from WAYLIVRA may be adversely affected.

We estimate there are 3,000 to 5,000 FCS patients and an additional 3,000 to 5,000 FPL patients globally. Our estimates of the sizes of the patient populations are based on published studies as well as internal analyses. If the results of these studies or our analyses of them do not accurately reflect the number of patients with FCS and FPL, our assessment of the market potential for WAYLIVRA may be inaccurate, making it difficult or impossible for us to meet our revenue goals, or to obtain and maintain profitability. In addition, as is the case with most orphan diseases, if we cannot successfully raise awareness of these diseases and improve diagnosis, it will be more difficult or impossible to achieve profitability.

In addition, since the patient populations for FCS and FPL are small, the per-patient drug pricing must be priced appropriately in order to recover our development and manufacturing costs, fund adequate patient support programs and achieve profitability. For these initial indications, we may not maintain or obtain sufficient sales volume at a price that justifies our product development efforts and our sales and marketing and manufacturing expenses.

The patient population suffering from hATTR amyloidosis is small and has not been established with precision. If the actual number of patients is smaller than we estimate, or if we cannot raise awareness of the disease and diagnosis is not improved, our revenue and ability to achieve profitability from either TEGSEDI or AKCEA-TTR-L _Rx may be adversely affected.

Our estimate of the sizes of the patient populations are based on published studies as well as internal analyses. If the results of these studies or our analyses of them do not accurately reflect the number of patients with hATTR amyloidosis, our assessment of the market potential for either TEGSEDI or AKCEA-TTR-L _Rx may be inaccurate, making it difficult or impossible for us to meet our revenue goals, or to obtain and maintain profitability. In addition, as is the case with most orphan diseases, if we cannot successfully raise awareness of these diseases and improve diagnosis, it will be more difficult or impossible to achieve profitability. For these initial indications, we may not maintain or obtain sufficient sales volume at a price that justifies our product development efforts and our sales and marketing and manufacturing expenses.

39

If we or our partners fail to compete effectively, WAYLIVRA, TEGSEDI and our other drugs in development will not contribute significant revenue.

Our competitors engage in drug discovery throughout the world, are numerous and include, among others, major pharmaceutical companies and specialized biopharmaceutical firms. Our competitors may succeed in developing drugs that are:

These competitive developments could make our drugs, including WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, obsolete or non-competitive. Further, all of our drugs are delivered by injection, which may render them less attractive to patients than non-injectable products offered by our current or future competitors.

Many of our competitors have substantially greater financial, technical and human resources than we do. In addition, many of these competitors have significantly greater experience than we do in conducting preclinical testing and human clinical studies, in obtaining FDA and other regulatory authorizations and in commercializing pharmaceutical products. Accordingly, our competitors may succeed in obtaining regulatory authorization for products earlier than we do. Marketing and sales capability is another factor relevant to the competitive position of our drugs, and many of our competitors will have greater marketing and sales capabilities than our capabilities.

There are several pharmaceutical and biotechnology companies engaged in the development or commercialization of products against targets that are also targets of drugs in our development pipeline. For example, if approved, WAYLIVRA could face competition from drugs like metreleptin and gemcabene. Metreleptin, produced by Novelion Therapeutics, Inc., is currently approved in the U.S. and E.U. for use in generalized lipodystrophy patients. WAYLIVRA may also compete with gemcabene, an oral small molecule that reduces apoC-III, that Gemphire Therapeutics, Inc. is developing to treat patients with triglycerides above 500 mg/dL.

As an additional example, TEGSEDI could face competition from drugs like ONPATTRO, marketed by Alnylam for hATTR amyloidosis with polyneuropathy in the U.S. and E.U. , tafamidis, available in the E.U. for stage 1 hATTR amyloidosis with polyneuropathy and under review in the U.S. for ATTR with cardiomyopathy, and AG10, which is being developed by Eidos for patients with ATTR with cardiomyopathy . For example, ONPATTRO is approved in the United States and Europe for a similar and broader indication as TEGSEDI. AG10, which recently completed its Phase 2 dose-finding study, is an orally administered TTR tetramer stabilizer for ATTR amyloidosis. If WAYLIVRA, TEGSEDI or the other drugs in our pipeline cannot compete effectively with these and other products with common or similar indications to the drugs in our pipeline, we may not be able to generate substantial revenue from our product sales.

If government or other third-party payors fail to provide adequate coverage and payment rates for TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, our revenue and prospects for profitability will be limited.

In both domestic and foreign markets, sales of our future products will depend in part upon the availability of coverage and reimbursement from third-party payors. The majority of patients in the United States who would fit within our target patient populations for our drugs have their healthcare supported by a combination of Medicare coverage, other government health programs such as Medicaid, managed care providers, private health insurers and other organizations. Coverage decisions may depend upon clinical and economic standards that disfavor new drug products when more established or lower cost therapeutic alternatives are already available or subsequently become available. Assuming coverage is approved, the resulting reimbursement payment rates might not be enough to make our drugs affordable. Accordingly, TEGSEDI and, if approved, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, will face competition from other therapies and drugs for limited financial resources. We may need to conduct post-marketing studies to demonstrate the cost-effectiveness of any future products to satisfy third-party payors. These studies might require us to commit a significant amount of management time and financial and other resources. Third-party payors may never consider our future products as cost-effective. Adequate third-party coverage and reimbursement might not be available to enable us to maintain price levels sufficient to realize an appropriate return on investment in product development.

40

Third-party payors, whether foreign or domestic, or governmental or commercial, are developing increasingly sophisticated methods of controlling healthcare costs. In addition, in the United States, no uniform policy of coverage and reimbursement for drug products exists among third-party payors. Therefore, coverage and reimbursement for drug products can differ significantly from payor to payor. Further, we believe that future coverage and reimbursement will likely be subject to increased restrictions both in the United States and in international markets. For example, in the United States, recent health reform measures have resulted in reductions in Medicare and other healthcare funding, and there have been several recent U.S. Congressional inquiries and proposed federal legislation designed to, among other things, reform government program reimbursement methodologies for drug products and bring more transparency to drug pricing. Third-party coverage and reimbursement for our products or drugs may not be available or adequate in either the United States or international markets, which would negatively affect the potential commercial success of our products, our revenue and our profits.

If we are found in violation of federal or state "fraud and abuse" laws or other healthcare laws and regulations, we may be required to pay a penalty and/or be suspended from participation in federal or state healthcare programs, which may adversely affect our business, financial condition and results of operation.

We may be subject to various federal and state laws pertaining to healthcare "fraud and abuse," including anti-kickback laws and false claims laws. Anti-kickback laws, among other things, make it illegal for a prescription drug manufacturer to pay, or offer to pay, a healthcare provider to refer, purchase or prescribe a particular drug. Due to the breadth of the statutory and regulatory provisions, it is possible that government authorities and others might challenge our practices under anti-kickback or other fraud and abuse laws. Moreover, recent healthcare reform legislation has strengthened these laws. In addition, false claims laws prohibit anyone from knowingly and willingly presenting, or causing to be presented for payment, to government third-party payors, including Medicare and Medicaid claims for reimbursed drugs that are false or fraudulent, claims for items or services not provided as claimed, or claims for medically unnecessary items or services. Our activities relating to the sale and marketing of our products may be subject to scrutiny under these laws. If we violated fraud and abuse laws, we could face a combination of:

Given the significant penalties and fines that the government can impose on companies and individuals if convicted, allegations of violations often result in settlements even if the company or individual being investigated admits no wrongdoing. Settlements often include significant civil sanctions, including fines and civil monetary penalties, and corporate integrity agreements. If the government were to allege or convict us or our executive officers of violating these laws, our business could be harmed. In addition, private individuals may bring similar actions under the False Claims Act. Our activities could be subject to challenge for the reasons discussed above and due to the broad scope of these laws and the increasing focus on these laws by law enforcement authorities. To the extent we have access to protected health information we could be subject to federal and state health information privacy and security laws, including without limitation, the Health Insurance Portability and Accountability Act of 1996, or HIPAA, as amended by the Health Information Technology for Economic and Clinical Health Act, which governs the conduct of certain electronic healthcare transactions and protects the security and privacy of protected health information. State health information privacy and security laws in certain circumstances are more stringent than HIPAA and many of the state laws differ from each other in significant ways and may not have the same effect, thus complicating compliance. Our failure to comply with applicable federal and state health information privacy and security laws could subject us to significant fines and multi-year corrective action plans. TEGSEDI commercially launched in the U.S. in the fourth quarter of 2018 and as such we are now required to report annually to Centers for Medicare and Medicaid Services certain information related to payments and other transfers of value we may provide to physicians and teaching hospitals. Further, an increasing number of state laws require manufacturers to make reports to states on pricing and marketing information. Many of these laws are unclear as to what is required to comply with the laws. Given the lack of clarity in laws and their implementation, our reporting actions could be subject to the penalty provisions of the pertinent state authorities.

Similar rigid restrictions related to anti-kickbacks and promoting and marketing medicinal products apply in the European Union and other countries. Authorities in these countries strictly enforce these restrictions. Even in those countries where we will not be directly responsible for promoting and marketing our products, inappropriate activity by any of our international commercialization partners we may have could harm us.

41

Risks Related to Dependence on Third Parties

We plan to substantially depend on our collaboration with Novartis to develop and commercialize AKCEA-APO(a)-L _Rx and AKCEA-APOCIII-L _Rx .

We have granted Novartis an exclusive option to exclusively license each of AKCEA-APO(a)-L _Rx and AKCEA-APOCIII-L _Rx pursuant to our strategic collaboration, option and license agreement with Novartis _. In February 2019, Novartis exercised its option to license AKCEA-APO(a)-L _Rx . We plan to substantially depend on Novartis to further develop and commercialize AKCEA-APO(a)-L _Rx and potentially AKCEA-APOCIII-L _Rx . We initiated this collaboration primarily to have Novartis:

Since Novartis has exercised its option to license AKCEA-APO(a)-L _Rx , we will rely on Novartis to further develop, obtain regulatory approvals for, and commercialize it. In general, we cannot control the amount and timing of resources that Novartis devotes to our strategic collaboration. If Novartis fails to use commercially reasonable efforts to further develop, obtain regulatory approvals for, or commercialize AKCEA-APO(a)-L _Rx , or if Novartis' efforts are not effective, our business may be negatively affected. Novartis could pursue other technologies or develop other drugs either on its own or in collaboration with others to treat the same diseases as we and Novartis plan to treat with AKCEA-APO(a)-L _Rx . Novartis could pursue these technologies and develop these other drugs at the same time as it is developing or commercializing AKCEA-APO(a)-L _Rx , and Novartis is not required to inform us of such activities.

If Novartis exercises its option to license AKCEA-APOCIII-L _Rx , we would rely on Novartis to further develop, obtain regulatory approvals for, and commercialize it. In general, we cannot control the amount and timing of resources that Novartis devotes to our strategic collaboration. If Novartis fails to use commercially reasonable efforts to further develop, obtain regulatory approvals for, or commercialize AKCEA-APOCIII-L _Rx , or if Novartis' efforts are not effective, our business may be negatively affected. Novartis could pursue other technologies or develop other drugs either on its own or in collaboration with others to treat the same disease as we and Novartis plan to treat with AKCEA-APOCIII-L _Rx . Novartis could pursue these technologies and develop these other drugs at the same time as it is developing or commercializing AKCEA-APOCIII-L _Rx and Novartis is not required to inform us of such activities.

Our strategic collaboration with Novartis may not continue for various reasons. Novartis can terminate our agreement at any time and is under no obligation to exercise the options we granted them. If Novartis stops developing or commercializing AKCEA-APO(a)-L _Rx , or does not exercise its option to license AKCEA-APOCIII-L _{Rx ,} we will have to seek additional sources for funding and may have to delay or reduce our development and commercialization plans for these drugs.

In addition, following Novartis’ exercise of its option to license AKCEA-APO(a)-L _Rx in February 2019 , and if Novartis exercises its option to license AKCEA-APOCIII-L _Rx , Novartis will be responsible for the long-term supply of drug substance and finished drug product for the licensed drug.

Our strategic collaboration with Novartis may not result in the successful commercialization of AKCEA-APO(a)-L _Rx or AKCEA-APOCIII-L _Rx . If Novartis does not successfully develop, manufacture or commercialize AKCEA-APO(a)-L _Rx or AKCEA-APOCIII-L _Rx , we may receive limited or no revenues for these drugs.

We plan to substantially depend on our collaboration with PTC Therapeutics to commercialize TEGSEDI and WAYLIVRA in Latin America and certain Caribbean countries.

In August 2018, we granted PTC Therapeutics International Limited the exclusive right to commercialize TEGSEDI and WAYLIVRA in Latin America and certain Caribbean countries. We plan to substantially depend on PTC to commercialize these drugs in those geographic markets.

42

In general, we cannot control the amount and timing of resources that PTC devotes to our strategic collaboration. If PTC fails to use commercially reasonable efforts to obtain regulatory approvals for, or commercialize these drugs, or if PTC ’ s efforts are not effective, our business may be negatively affected. PTC could pursue other technologies or develop other drugs either on its own or in collaboration with others to treat the same diseases as we and PTC plan to treat with TEGSEDI and WAYLIVRA. PTC could pursue these technologies and develop these other drugs at the same time as it is developing or commercializing TEGSEDI and WAYLIVRA, and PTC is not required to inform us of such activities.

Our strategic collaboration with PTC may not continue for various reasons. If PTC stops commercializing a drug, we will have to seek additional sources for funding and may have to delay or reduce our commercialization plans for TEGSEDI and WAYLIVRA in Latin America or certain Caribbean countries.

Our strategic collaboration with PTC may not result in the successful commercialization of TEGSEDI or WAYLIVRA in Latin America or certain Caribbean countries. If PTC does not successfully commercialize TEGSEDI or WAYLIVRA, we may receive limited revenue for TEGSEDI or no revenue for WAYLIVRA in Latin America or certain Caribbean countries.

AKCEA-APOCIII-L _Rx and AKCEA-ANGPTL3-L _Rx may compete with WAYLIVRA, which could reduce our expected revenues for WAYLIVRA.

WAYLIVRA and AKCEA-APOCIII-L _Rx both inhibit the production of the same protein. We believe the enhancements we incorporated into AKCEA-APOCIII-L _Rx can provide greater patient convenience by allowing for significantly lower doses and less frequent administration compared to WAYLIVRA. As such, if Novartis exercises its option and successfully commercializes AKCEA-APOCIII-L _Rx while we are commercializing WAYLIVRA, to the extent physicians and patients elect to use AKCEA-APOCIII-L _Rx instead of WAYLIVRA, it will reduce the revenue we derive from WAYLIVRA. In addition, while AKCEA-ANGPTL3-L _Rx and WAYLIVRA use different mechanisms of action, if AKCEA-ANGPTL3-L _Rx can effectively lower triglyceride levels in FCS patients, it may likewise reduce the revenue we derive from WAYLIVRA.

If we cannot manufacture our drugs or contract with a third party to manufacture our drugs at costs that allow us to charge competitive prices to buyers, we will not be able to operate profitably.

To successfully commercialize TEGSEDI and, if approved, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, we will need to optimize and manage large-scale commercial manufacturing capabilities either on our own or through a third-party manufacturer. In addition, as our drug development pipeline matures, we will have a greater need for clinical study and commercial manufacturing capacity. We have no direct experience manufacturing pharmaceutical products of the chemical class represented by our drugs, called oligonucleotides, on a commercial scale for the systemic administration of a drug. We currently rely and expect to rely for the foreseeable future on Ionis' manufacturing capacity and efficiency and the capacity and efficiency of third parties to produce our oligonucleotide drugs, and our business could be negatively affected if Ionis and these third parties ceased to provide us with this capability for any reason. In addition, there are a small number of suppliers for certain raw materials that we use to manufacture our drugs, and some of these suppliers will need to increase their scale of production to meet our projected needs for commercial manufacturing. Further, if we cannot continue to acquire raw materials from these suppliers on commercially reasonable terms or at all, we may be required to find alternative suppliers, which could be expensive and time consuming and negatively affect our ability to develop or commercialize our drugs in a timely manner or at all. We may not be able to manufacture our drugs at a cost or in quantities necessary to make commercially successful products.

We do not have long-term supply agreements for our drugs. We cannot guarantee that we will have a steady supply of drug to complete clinical studies, make registration batches for approval or satisfy market demand if commercialized at prices that are commercially acceptable. In addition, if we need to change manufacturers for any reason, we will need to verify that the new manufacturer maintains facilities and procedures that comply with quality standards and with all applicable regulations and guidelines. The delays associated with verifying a new manufacturer could negatively affect our ability to develop drugs in a timely manner or within budget.

Also, manufacturers must adhere to the FDA's current Good Manufacturing Practices regulations and similar regulations in foreign countries, which the applicable regulatory authorities enforce through facilities inspection programs. Our contract manufacturers may not comply or maintain compliance with Good Manufacturing Practices, or similar foreign regulations. Non-compliance could significantly delay or prevent receipt of marketing authorization for our drugs, including authorizations for WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, or result in enforcement action after authorization that could limit the commercial success of our drugs, including WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development.

43

We depend on Ionis and third parties to conduct our clinical studies for our drugs and any failure of those parties to fulfill their obligations could adversely affect our development and commercialization plans.

We depend on Ionis and independent clinical investigators, contract research organizations and other third-party service providers to conduct the clinical studies for our drugs and expect to continue to do so in the future. For example, we use clinical research organizations for the clinical studies for WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development. We rely heavily on these parties for successful execution of our clinical studies, but do not control many aspects of their activities. For example, the investigators are not our employees. However, we are responsible for ensuring that these third parties conduct each of our clinical studies in accordance with the general investigational plan, approved protocols for the study and applicable regulations. Ionis and third parties may not complete activities on schedule or may not conduct our clinical studies in accordance with regulatory requirements or our stated protocols. The failure of these parties to carry out their obligations or a termination of our relationship with these third parties could delay or prevent the development, marketing authorization and commercialization of our drugs, including authorizations for WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development.

We may seek to form additional partnerships in the future with respect to WAYLIVRA, and our other drugs in development, and we may not realize the benefits of such partnerships.

Although we intend to develop and commercialize WAYLIVRA for patients with FCS and FPL ourselves, we may form partnerships, create joint ventures or collaborations or enter into licensing arrangements with third parties for the development and commercialization of our drugs in development. For example, we have granted PTC an exclusive license to commercialize WAYLIVRA in Latin America and certain Caribbean countries. We face significant competition in seeking appropriate strategic partners and the negotiation process is time-consuming and complex. Any delays in entering into new strategic partnership agreements related to our drugs could delay the development and commercialization of our drugs and reduce their competitiveness even if they reach the market. Moreover, we may not be successful in our efforts to establish other strategic partnerships or other collaborative arrangements for any additional drugs because the potential partner may consider that our development pipeline is not advanced enough to justify a collaborative effort, or that WAYLIVRA and our other drugs in development do not have the requisite potential to demonstrate safety and efficacy in the target populations in other geographic markets. In addition, we will need to mutually agree with Ionis on the terms of any additional sublicenses to a third party for WAYLIVRA and our other drugs in development. If we cannot mutually agree on terms for a sublicense to a third party or if Ionis does not agree to a sublicense at all, it could delay our ability to develop and commercialize WAYLIVRA and our other drugs in development. Even if we are successful in establishing such a strategic partnership or collaboration, we cannot be certain that, following such a strategic transaction or collaboration, we will be able to progress the development and commercialization of the applicable drugs as envisioned, or that we will achieve the revenue that would justify such transaction. If we do not accurately evaluate the commercial potential or target market for a particular drug, we may relinquish valuable rights to that drug through future collaboration, licensing or other arrangements in cases in which it would have been more advantageous for us to retain sole development and commercialization rights.

Risks Related to Our Relationship with Ionis

Ionis controls the direction of our business, and the concentrated ownership of our common stock will prevent you and other stockholders from influencing significant decisions.

Ionis owns 67,383,965 shares of our common stock, or approximately 75 percent, of the economic interest and voting power of our outstanding common stock as of February 20, 2019, which ownership will be expected to increase further if we achieve certain milestone events and pay the associated milestone payment in shares of common stock pursuant to the payment election. As long as Ionis beneficially controls a majority of the voting power of our outstanding common stock, it will generally be able to determine the outcome of all corporate actions requiring stockholder approval, including the election and removal of directors. Even if Ionis were to control less than a majority of the voting power of our outstanding common stock, it may influence the outcome of such corporate actions so long as it owns a significant portion of our common stock. If Ionis continues to hold its shares of our common stock, it could remain our controlling stockholder for an extended period of time or indefinitely.

The licensing transaction with Ionis and the common stock issuances in connection with the achievement of the TEGSEDI regulatory milestones has increased Ionis ’ ownership percentage, and this increase, along with Ionis ’ increased reliance on Akcea as a commercialization partner, given that Akcea could now be commercializing at least two Ionis-developed products (WAYLIVRA and TEGSEDI), may increase the length of time during which Ionis will control us. As a general matter, the TEGSEDI license agreement and the related Investor Rights Agreement increased Ionis ’ control over our affairs. In addition, our TEGSEDI licensing agreement requires Ionis ’ consent to the budget related to the commercialization of TEGSEDI and AKCEA-TTR-L _Rx .

44

Ionis' interests may not be the same as, or may conflict with, the interests of our other stockholders. You will not be able to affect the outcome of any stockholder vote while Ionis controls the majority of the voting power of our outstanding common stock. As a result, Ionis can control, directly or indirectly and subject to applicable law, all matters affecting us, including:

Because Ionis' interests may differ from ours or yours, actions that Ionis takes with respect to us, as our controlling stockholder, may not be favorable to us or you.

As a “controlled company” under the marketplace rules of the Nasdaq Stock Market, we may rely on exemptions from certain corporate governance requirements that provide protection to stockholders of companies that are subject to such requirements.

Ionis beneficially owns more than 50% of the voting power of our outstanding common stock. As a result, we are a “ controlled company ” under the marketplace rules of the Nasdaq Stock Market, or Nasdaq, and eligible to rely on exemptions from Nasdaq corporate governance requirements generally obligating listed companies to maintain:

Currently, a majority of our board is made up of independent directors. As a controlled company, we have and in the future may avail ourselves of some of these exemptions. Accordingly, our stockholders may not have the same protections afforded to stockholders of companies that are subject to the Nasdaq corporate governance requirements described above.

If Ionis sells a controlling interest in our company to a third party in a private transaction, you may not realize a change of control premium on shares of our common stock, and we may become subject to the control of a presently unknown third party.

Ionis owns a significant equity interest in our company. This means that Ionis could choose to sell some or all of its shares of our common stock in a privately negotiated transaction, which, if sufficient in size, could result in a change of control of our company.

Ionis' ability to privately sell its shares of our common stock, with no requirement for a concurrent offer to be made to acquire your shares of our common stock, could prevent you from realizing any change of control premium on your shares of our common stock that may otherwise accrue to Ionis on its private sale of our common stock. Additionally, if Ionis privately sells its significant equity interest in our company, we may become subject to the control of a presently unknown third party. Such third party may have conflicts of interest with those of other stockholders. In addition, if Ionis sells a controlling interest in our company to a third party, such a sale could negatively impact or accelerate any future indebtedness we may incur, and negatively impact any other commercial agreements and relationships, all of which may adversely affect our ability to run our business as described herein and may have a material adverse effect on our operating results and financial condition.

45

Certain of our directors and officers may have actual or potential conflicts of interest because of their positions with Ionis.

Damien McDevitt, Chief Business Officer for Ionis, and B. Lynne Parshall, Senior Strategic Advisor and board member for Ionis, serve on our board of directors and retain their positions or engagements with Ionis. In addition, these individuals own Ionis equity and Ionis equity awards. Ionis common stock, options to purchase Ionis common stock and other Ionis equity awards represent a significant portion of these individuals' net worth. Their position at Ionis and the ownership of any Ionis equity or equity awards creates, or may create the appearance of, conflicts of interest when we ask these individuals to make decisions that could have different implications for Ionis than the decisions have for us. In addition, our certificate of incorporation provides for the allocation of certain corporate opportunities between us and Ionis. Under these provisions, neither Ionis or its other affiliates, nor any of their officers, directors, agents or stockholders, will have any obligation to present to us certain corporate opportunities. For example, a director of our company who also serves as a director, officer or employee of Ionis or any of its other affiliates may present to Ionis certain acquisitions, in-licenses, potential development programs or other opportunities that may be complementary to our business and, as a result, such opportunities may not be available to us. To the extent attractive corporate opportunities are allocated to Ionis or its other affiliates instead of to us, we may not be able to benefit from these opportunities.

The resources Ionis provides us under the license agreements and the services agreement may not be sufficient for us to operate as a standalone company, and we may experience difficulty in separating our resources from Ionis.

Because we have not operated separately from Ionis in the past, we may have difficulty doing so. We will need to acquire resources in addition to, and eventually in lieu of, those provided by Ionis to our company, and may also face difficulty in separating our resources from Ionis' resources and integrating newly acquired resources into our business. In addition, Ionis may prioritize its own research, development, manufacturing and other needs ahead of the services Ionis has agreed to provide us, or Ionis employees who conduct services for us may prioritize Ionis' interests over our interests. Our business, financial condition and results of operations could be harmed if we have difficulty operating as a standalone company, fail to acquire resources that prove to be important to our operations or incur unexpected costs in separating our resources from Ionis' resources or integrating newly acquired resources.

We may not realize the benefits of the licensing transaction with Ionis if we are unable to successfully transition, integrate and support the development and commercialization of TEGSEDI and AKCEA-TTR-L _Rx .

As a result of the licensing transaction with Ionis, we need to successfully transition, integrate and support the assets we acquired related to the commercialization and development of TEGSEDI and AKCEA-TTR-L _Rx if we are to realize any of the potential benefits of the licensing transaction. The failure to meet these integration challenges, including the addition of TEGSEDI commercial team and other employees from Ionis and the coordination across geographies between our headquarters in Massachusetts and our commercialization team in other locations, including major global markets, could seriously harm our results of operations. Our failure to implement an orderly integration could result in failure of, or delays in, the development or commercialization of TEGSEDI and AKCEA-TTR-L _Rx . Such failure or delay could adversely impact our business, results of operations, financial condition and prospects for future growth.

We will incur incremental costs as a standalone company.

Ionis currently performs or supports many important corporate functions for our company. Our consolidated financial statements reflect charges for these services on an allocation basis. Under our services agreement with Ionis we can use these Ionis services for a fixed term established on a service-by-service basis. However, we generally will have the right to terminate a service earlier if we give notice to Ionis. Partial reduction in the provision of any service requires Ionis' consent. In addition, either party will be able to terminate the agreement due to a material breach of the other party, upon prior written notice, subject to limited cure periods.

46

We will pay Ionis mutually agreed upon fees for these services, based on Ionis' costs of providing the services. Since we negotiated the services agreement in the context of a parent subsidiary relationship, the terms of the agreement, including the fees charged for the services, may be higher or lower than those that would be agreed to by parties bargaining at arm's length for similar services and may be higher or lower than the costs reflected in the allocations in our historical consolidated financial statements. Ionis will pass third party costs through to us at Ionis' cost. In addition, while Ionis provides us these services, our operational flexibility to modify or implement changes with respect to such services or the amounts we pay for them will be limited.

We may not be able to replace these services or enter into appropriate third-party agreements on terms and conditions, including cost, comparable to those that we will receive from Ionis under our services agreement. Additionally, after the agreement terminates, we may not sustain the services at the same levels or obtain the same benefits as when we were receiving such services and benefits from Ionis. When we begin to operate these functions separately, if we do not have our own adequate systems and business functions in place, or cannot obtain them from other providers, we may not operate our business effectively or at comparable costs, and our business may suffer. In addition, we have historically received informal support from Ionis, which may not be addressed in our services agreement. The level of this informal support will diminish and could end in the future.

We may not be able to fully realize the expected benefits of our license agreements with Ionis.

We have development, commercialization and license agreements with Ionis pursuant to which, subject to certain restrictions, we and Ionis will share development responsibilities for WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development. We are paying for research and development costs and reimbursing Ionis for Ionis' employees supporting our development activities. Until we build or acquire our own capabilities to replace those Ionis is providing to us, particularly development, regulatory and manufacturing services, we will be heavily dependent on Ionis.

While we and Ionis intend the license agreements, on the whole, to bolster our capabilities, certain terms of the license agreements and the other related agreements with Ionis may limit our ability to achieve the expected benefits of these transactions, including:

Each of the foregoing terms and Ionis' other rights under the license agreements, could limit our ability to realize the expected benefits of the license agreements or otherwise limit our ability to pursue transactions or development efforts other stockholders may view as beneficial. Further, if Ionis does not continue to own a significant portion of our equity, Ionis' incentive to help us would be diminished. If we fail to achieve the expected benefits of our agreements with Ionis, it may be more difficult, time consuming or expensive for us to develop and commercialize WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development and continue the commercialization of TEGSEDI, or may result in our drugs being later to market than those of our competitors or prevent them from ever getting to market. If these events cause delays in new product development we could lose the first in class products in a given therapeutic area.

47

Risks Related to Our Intellectual Property

If we breach our obligations under any of our license agreements with Ionis, we could lose our rights to WAYLIVRA, TEGSEDI, AKCEA-TTR-L _Rx and our other drugs in development.

We obtained our rights to WAYLIVRA, TEGSEDI, AKCEA-TTR-L _Rx and our other drugs in development under our license agreements with Ionis. If we breach our obligations under these license agreements and, as a result, Ionis subsequently exercises its right to terminate it, we generally would not be able to continue to develop or commercialize TEGSEDI, WAYLIVRA, AKCEA-TTR-L _Rx and our other drugs in development that incorporate Ionis' intellectual property, and Ionis would receive a royalty-free, nonexclusive license to our improvements to those programs, meaning we would lose the benefits of our investment in these programs. If we breach our obligations under the license agreement with respect to AKCEA-APO(a)-L _Rx or AKCEA-APOCIII-L _Rx and, as a result, Ionis exercises its right to terminate it, then our strategic collaboration with Novartis would convert into a direct strategic collaboration between Novartis and Ionis, and Ionis would receive all of the revenue and other benefits associated with that strategic collaboration. Similarly, if we breach our obligations under the license agreement with respect to TEGSEDI or AKCEA-TTR-L _Rx and, as a result, Ionis exercises its right to terminate it, then our strategic collaboration with PTC in Latin America and certain Caribbean countries would convert into a direct strategic collaboration between PTC and Ionis, and Ionis would receive all of the revenue and other benefits associated with that strategic collaboration.

If we cannot protect our patent rights or our other proprietary rights, others may compete more effectively against us.

Our success depends to a significant degree upon whether we can continue to secure and maintain intellectual property rights that protect TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development. However, patents may not issue from any of our pending patent applications in the United States or in other countries and we may not be able to obtain, maintain or enforce our owned or licensed patents and other intellectual property rights which could impact our ability to compete effectively. In addition, the scope of any of our owned or licensed patents may not be sufficiently broad to provide us with a competitive advantage. Furthermore, other parties may successfully challenge, invalidate or circumvent our issued patents or patents licensed to us so that our patent rights do not create an effective competitive barrier or revenue source.

Composition of matter patents on the active pharmaceutical ingredient for a product are generally considered to be the strongest form of intellectual property protection for pharmaceutical products, as such patents provide protection without regard to any method of use. Our WAYLIVRA patent portfolio currently includes:

The natural term of the issued U.S. patent covering the WAYLIVRA composition of matter will expire in 2023, but we plan to seek to extend the U.S. patent expiration beyond 2023 based upon the development and regulatory review period in the United States. The natural term of the granted European and Australian patents covering WAYLIVRA will expire in 2024, but we plan to seek to extend each of these patents beyond 2024 based upon the development and regulatory review periods in Europe and Australia.

The natural term of the last expiring issued U.S. patent covering the composition of matter of TEGSEDI will expire in 2031. Patents issued in other countries will have the same natural term. We plan to seek to extend the term of one patent covering TEGSEDI in the U.S., if approved, and any other jurisdictions where such extension is available, based upon the development and regulatory review periods for TEGSEDI and in accordance with applicable laws.

We cannot be certain that the U.S. Patent and Trademark Office, or U.S. PTO, and courts in the United States or the patent offices and courts in foreign countries will consider the claims in our owned or licensed patents and applications covering WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx , AKCEA-TTR-L _Rx and our other drugs in development as patentable. Method-of-use patents protect the use of a product for the specified method. This type of patent does not prevent a competitor from making and marketing a product that is identical to our product for an indication that is outside the scope of the patented method. Moreover, even if competitors do not actively promote their product for our targeted indications, physicians may prescribe these products off-label. Although off-label prescriptions may infringe or contribute to the infringement of method-of-use patents, the practice is common and such infringement is difficult to prevent, including through legal action.

48

If we or any licensor partner loses or cannot obtain patent protection for TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx or our other drugs in development it could have a material adverse impact on our business.

Intellectual property litigation could cause us to spend substantial resources and prevent us from pursuing our programs.

From time to time we may have to defend our intellectual property rights. If we are involved in an intellectual property dispute, we may need to litigate to defend our rights or assert them against others. Disputes can involve arbitration, litigation or proceedings declared by the U.S. PTO or the International Trade Commission or foreign patent authorities. Even if resolved in our favor, litigation or other legal proceedings relating to intellectual property claims may cause us to incur significant expenses, and could distract our technical and management personnel from their normal responsibilities. In addition, there could be public announcements of the results of hearings, motions or other interim proceedings or developments and if securities analysts or investors perceive these results to be negative, it could have a substantial adverse effect on the price of our common stock. Such litigation or proceedings could substantially increase our operating losses and reduce the resources available for development activities or any future sales, marketing or distribution activities. We may not have sufficient financial or other resources to adequately conduct such litigation or proceedings. Some of our competitors may be able to sustain the costs of such litigation or proceedings more effectively than we can because of their greater financial resources and more mature and developed intellectual property portfolios.

Third parties may initiate legal proceedings alleging that we are infringing their intellectual property rights, the outcome of which would be uncertain and could have a material adverse effect on the success of our business.

Our commercial success depends upon our ability and the ability of our strategic partners to develop, manufacture, market and sell our drugs and use our proprietary technologies without infringing the proprietary rights and intellectual property of third parties. Extensive litigation regarding patents and other intellectual property rights is common in the biotechnology and pharmaceutical industries. We may in the future become party to, or threatened with, adversarial proceedings or litigation regarding intellectual property rights with respect to our drugs and technology, including interference, derivation, reexamination, post-grant review, opposition, cancellation or similar proceedings before the U.S. PTO or its foreign counterparts.

Third parties may assert infringement claims against us based on existing patents or patents that may be granted in the future. For example, a potential competitor was issued a patent which they have broadly characterized in their annual report on Form 10-K for the year ended December 31, 2017 as being directed to single-stranded antisense polynucleotide molecules capable of inhibiting expression of the human transthyretin gene, and having certain combinations of structural features. This third party has also attempted to broadly characterize certain other patents that they hold. While we believe that we would have substantial defenses in the event this competitor brought a claim against us with respect to TEGSEDI or AKCEA-TTR-L _Rx , patent litigation is inherently uncertain, involves substantial cost and is a distraction to management. Moreover, our stock price may be impacted by the existence of or developments during a litigation, even developments that are preliminary in nature.

We may not be aware of all such intellectual property rights potentially relating to our drugs and their uses. If a third party claims that WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx , AKCEA-TTR-L _Rx , our other drugs in development or our technology infringe its patents or other intellectual property rights, we or our partners may have to discontinue an important product or product line, alter our products and processes, pay license fees or cease certain activities. We may not be able to obtain a license to needed intellectual property on favorable terms, if at all. There are many patents issued or applied for in the biotechnology industry, and we may not be aware of patents or patent applications held by others that relate to our business. This is especially true since patent applications in the United States are filed confidentially for the first 18 months. Moreover, the validity and breadth of biotechnology patents involve complex legal and factual questions for which important legal issues remain. Thus, we do not know with certainty that our drugs or our intended commercialization thereof, does and will not infringe or otherwise violate any third party's intellectual property.

We will not seek to protect our intellectual property rights in all jurisdictions throughout the world and we may not be able to adequately enforce our intellectual property rights even in the jurisdictions where we seek protection.

Filing, prosecuting and defending patents on our drugs in all countries and jurisdictions throughout the world would be prohibitively expensive, and our intellectual property rights in some countries outside the United States could be less extensive than those we could obtain in the United States. In addition, the laws of some foreign countries do not protect intellectual property rights to the same extent as laws in the United States. Consequently, we may not be able to prevent third parties from practicing our inventions in all countries outside the United States, or from selling or importing products made using our inventions in and into the United States or other jurisdictions.

49

Competitors may use our technologies in jurisdictions where we do not pursue and obtain patent protection to develop their own products. In addition, competitors may export otherwise infringing products to territories where we have patent protection, but enforcement is not as strong as that in the United States. These products may compete with our products and our patent rights or other intellectual property rights may not be effective or sufficient to prevent them from competing. Even if we pursue and obtain issued patents in particular jurisdictions, our patent claims or other intellectual property rights may not be effective or sufficient to prevent third parties from so competing.

The laws of some foreign countries do not protect intellectual property rights to the same extent as the laws of the United States. Many companies have encountered significant problems in protecting and defending intellectual property rights in certain foreign jurisdictions. The legal systems of some countries, particularly developing countries, do not favor the enforcement of patents and other intellectual property protection, especially those relating to biotechnology. This could make it difficult for us to stop competitors from infringing our patent rights or misappropriating our other intellectual property rights. For example, many foreign countries have compulsory licensing laws under which a patent owner must grant licenses to third parties. In addition, many countries limit our right to enforce our patent rights against third parties, including government agencies or government contractors. In these countries, patents may provide limited or no benefit. We must ultimately seek patent protection on a country-by-country basis, which is an expensive and time-consuming process with uncertain outcomes. Accordingly, we may choose not to seek patent protection in certain countries, and we will not have the benefit of patent protection in such countries.

In addition, proceedings to enforce our patent rights in foreign jurisdictions could result in substantial costs and divert our efforts and attention from other aspects of our business, could put our patent rights at risk of being invalidated or interpreted narrowly, could put our owned or licensed patent applications at risk of not issuing and could provoke third parties to assert claims against us. We may not prevail in any lawsuits that we initiate and the damages or other remedies awarded, if any, may not be commercially meaningful. Accordingly, our efforts to enforce our intellectual property rights around the world may be inadequate to obtain a significant commercial advantage from the intellectual property that we develop or license.

If we do not obtain additional protection under the Hatch-Waxman Amendments and similar foreign legislation by extending the patent protection for TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx , and our other drugs in development, our business may be materially harmed.

Depending upon the timing, duration and specifics of the first FDA marketing authorization of TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx , and our other drugs in development, a United States patent that we own or license may be eligible for limited patent term restoration under the Drug Price Competition and Patent Term Restoration Act of 1984, referred to as the Hatch-Waxman Amendments. The Hatch-Waxman Amendments allow the owner of an approved product to extend patent protection for up to five years as compensation for patent term lost during product development and the FDA regulatory review process. During this period of extension, the scope of protection is limited to the approved product and approved uses.

In 2018 we applied for patent term extensions to U.S. patents covering the TEGSEDI compound, composition and uses to recapture a portion of the term lost during regulatory review. Although we have applied for patent term extension for TEGSEDI, and plan on seeking patent term restoration for our other products, we may not succeed if, for example, we fail to apply within applicable deadlines, fail to apply prior to expiration of relevant patents or otherwise fail to satisfy applicable requirements. Moreover, the applicable time period or the scope of patent protection afforded could be less than we request. If we cannot obtain patent term restoration or the term of any such patent restoration is less than we request, our competitors may enter the market and compete against us sooner than we anticipate, and our ability to generate revenue could be materially adversely affected.

Changes in United States patent law could diminish the value of patents in general, thereby impairing our ability to protect our products.

Recent United States Supreme Court rulings have narrowed the scope of patent protection available in certain circumstances and weakened the rights of patent owners in certain situations. In addition to increasing uncertainty with regard to our ability to obtain patents in the future, this combination of events has created uncertainty with respect to the value of patents, once obtained. Depending on decisions by the United States Congress, the federal courts, and the U.S. PTO, the laws and regulations governing patents could change in unpredictable ways that would weaken our ability to obtain new patents or to enforce our existing patents and patents that we might obtain in the future.

50

If we and our partners do not adequately protect the trademarks and trade names for our products, then we and our partners may not be able to build name recognition in our markets of interest and our business may be adversely affected.

Our competitors or other third parties may challenge, infringe or circumvent the trademarks or trade names for our products. We and our partners may not be able to protect these trademarks and trade names. In addition, if the trademarks or trade names for one of our products infringe the rights of others, we or our partners may be forced to stop using the trademarks or trade names, which we need for name recognition in our markets of interest. If we cannot establish name recognition based on our trademarks and trade names, we and our partners may not be able to compete effectively and our business may be adversely affected.

Intellectual property rights do not necessarily address all potential threats to our competitive advantage.

The degree of future protection afforded by our intellectual property rights is uncertain because intellectual property rights have limitations, and may not adequately protect our business, or permit us to maintain our competitive advantage. The following examples are illustrative:

Should any of these events occur, they could significantly harm our business, results of operations and prospects.

Risks Related to Our Business and Industry

We will need to significantly increase the size of our organization, and we may experience difficulties in managing growth.

We are currently a small company. To continue the commercialization of TEGSEDI and commercialize our drugs in development that we are responsible for commercializing, we will need to increase our operations and expand our use of third-party contractors. We plan to continue to build our compliance, financial and operating infrastructure to ensure the maintenance of a well-managed company including hiring additional staff within our regulatory, clinical and medical affairs groups and an in-house commercial organization initially focused on marketing and selling TEGSEDI and, if approved, WAYLIVRA. We have added a significant number of new employees to our sales and marketing capability to commercialize TEGSEDI.

We may also anticipate needs for growth that do not materialize. For example, in anticipation of WAYLIVRA ’ s potential approval, we added a significant number of new employees to our sales and marketing capability to develop WAYLIVRA in the second half of 2017. However, as a result of our receipt of a complete response letter, or CRL, from the FDA regarding the new drug application for WAYLIVRA, on September 6, 2018, we enacted a plan to reorganize our workforce to better align with the immediate needs of our business. In connection with this reorganization plan, we reduced our workforce by approximately 12%. If WAYLIVRA is subsequently approved in the United States, we will again need to increase our operations and expand our use of third-party contractors. We cannot assure you that we will not build out our compliance, financial or operating infrastructure again in anticipation of developments that do not occur or that occur later than we anticipate.

51

The current and future growth will impose significant added responsibilities on our management, including the need to maintain, integrate, optimize and manage additional employees. In addition, to meet our obligations as a public company, we will need to increase our general and administrative capabilities. Our current management, personnel and systems may not be adequate to support this growth. Our future financial performance and our ability to commercialize our drugs and to compete effectively will depend, in part, on our ability to manage any future growth effectively. To that end, we must be able to:

Our staff, financial resources, systems, procedures or controls may be inadequate to support our operations and our management may be unable to successfully manage future market opportunities or our relationships with customers and other third parties.

If we do not progress in our programs as anticipated, the price of our securities could decrease.

For planning purposes, we estimate and may disclose the timing of a variety of clinical, regulatory and other milestones, such as when we anticipate a certain drug will enter into clinical trials, when we anticipate completing a clinical study, when we anticipate filing an application for marketing authorization, or when we or our partners plan to commercially launch a drug. We base our estimates on present facts and a variety of assumptions. Many underlying assumptions are outside of our control. If we do not achieve milestones in accordance with our or our investors' or securities analysts' expectations, including milestones related to WAYLIVRA, TEGSEDI, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development, the price of our securities could decrease.

The loss of key personnel, or if we cannot attract and retain highly skilled personnel, could make it more difficult to run our business and reduce our likelihood of success.

We are dependent on the principal members of our management and scientific staff. We do not have employment agreements with any of our executive officers that would prevent them from leaving us. The loss of management and key scientific employees might slow the achievement of important research and development goals. It is also critical to our success that we recruit and retain qualified scientific personnel to perform development work and marketing, sales and commercial support personnel to perform commercialization activities. We may not be able to attract and retain skilled and experienced scientific and commercial personnel on acceptable terms because of intense competition for experienced personnel among many pharmaceutical and health care companies, universities and non-profit research institutions. In addition, failure to successfully complete clinical studies, obtain regulatory approvals or effectively commercialize drugs may make it more challenging to recruit and retain qualified personnel.

We are exposed to potential product liability claims, and insurance against these claims may not be available to us at a reasonable rate in the future or at all.

Our business exposes us to potential product liability risks that are inherent in the testing, manufacturing, marketing and sale of therapeutic products, including potential product liability claims related to TEGSEDI, WAYLIVRA, AKCEA-APO(a)-L _Rx, AKCEA-TTR-L _Rx and our other drugs in development. We have clinical study insurance coverage and commercial product liability insurance coverage. In addition, Novartis has agreed to indemnify us against specific claims arising from Novartis' development and commercialization of AKCEA-APO(a)-L _Rx and AKCEA-APOCIII-L _Rx , and PTC has agreed to indemnify us against specific claims arising from PTC ’ s commercialization of TEGSEDI and WAYLIVRA in Latin America and certain Caribbean countries. However, this insurance coverage and indemnities may not be adequate to cover claims against us. Insurance may not be available to us at an acceptable cost, if at all. Regardless of their merit or eventual outcome, products liability claims may result in decreased demand for our drug products, injury to our reputation, withdrawal of clinical study volunteers and loss of revenue. Thus, whether or not we are insured or indemnified, a product liability claim or product recall may result in losses that could be material.

52

Because we use biological materials, hazardous materials, chemicals and radioactive compounds, if we do not comply with laws regulating the protection of the environment and health and human safety, our business could be adversely affected.

Our development and manufacturing activities involve the use of potentially harmful biological materials as well as materials, chemicals and various radioactive compounds that could be hazardous to human health and safety or the environment. We cannot completely eliminate the risk of contamination, which could cause:

In such an event, we may be held liable for any resulting damages, and any liability could exceed our resources. Although we carry insurance in amounts and types that we consider commercially reasonable, we do not have insurance coverage for losses relating to an interruption of our development, manufacturing or commercialization efforts caused by contamination, and the coverage or coverage limits of our insurance policies may not be adequate. If our losses exceed our insurance coverage, our financial condition would be adversely affected.

A variety of risks associated with operating our business and marketing our drugs internationally could materially adversely affect our business.

In addition to our U.S. operations, we are commercializing TEGSEDI in Europe and Canada and, following approval, plan to establish operations to commercialize our products in other countries globally. We face risks associated with our current and planned international operations, including possible unfavorable regulatory, pricing and reimbursement, political, tax and labor conditions, which could harm our business. Because we have international operations we are subject to numerous risks associated with international business activities, including:

53

The United Kingdom’s anticipated exit from the EU could increase these risks.

Our business activities outside of the United States are subject to the FCPA and similar anti-bribery or anti-corruption laws, regulations or rules of other countries in which we operate, including the United Kingdom's Bribery Act 2010. In many other countries, the healthcare providers who prescribe pharmaceuticals are employed by their government, and the purchasers of pharmaceuticals are government entities; therefore, any dealings with these prescribers and purchasers may be subject to regulation under the FCPA. There is no certainty that all employees and third-party business partners (including our distributors, wholesalers, agents, contractors and other partners) will comply with anti-bribery laws. In particular, we do not control the actions of manufacturers and other third-party agents, although we may be liable for their actions. Violation of these laws may result in civil or criminal sanctions, which could include monetary fines, criminal penalties, and disgorgement of past profits, which could have a material adverse impact on our business and financial condition.

The impact on us of the vote by the United Kingdom to leave the European Union cannot be predicted.

On June 23, 2016, the United Kingdom, or the UK, voted to leave the EU in an advisory referendum, which is generally referred to as Brexit. On March 29, 2017, the UK delivered notice under Article 50 of the Lisbon Treaty of its intent to leave the EU, beginning a two year negotiation period for the UK and the 27 remaining members of the EU to reach agreement on the terms of Brexit. The UK is a significant pharmaceutical market, and Brexit may lead to legal uncertainty and potentially divergent laws and regulations between the UK and the EU as the UK determines which EU laws to replicate or replace. We cannot predict whether or not the UK will significantly alter its current laws and regulations in respect of the pharmaceutical industry and, if so, what impact any such alteration would have on us or our business.

As part of Brexit, the EMA, currently situated in London, is expected to relocate to Amsterdam. There is a risk that the relocation process will interrupt current administrative routines and occupy resources, which may lead to delays in the EMA’s handling of our WAYLIVRA application and generally adversely affect our dealings with the EMA. Further, there is considerable uncertainty resulting from a lack of precedent and the complexity of the UK and EU’s intertwined legal regimes as to how Brexit will impact the life sciences industry in Europe, including our company, including with respect to ongoing or future clinical trials. The impact will largely depend on the model and means by which the UK’s relationship with the EU is governed post‑Brexit. For example, following Brexit, the UK will no longer be covered by the centralized procedures for obtaining EU-wide marketing authorization from the EMA and, unless a specific agreement is entered into, a separate process for authorization of drug products, including our product candidates, will be required in the UK, the potential process for which is currently unclear. Brexit may adversely affect and delay our ability to commercialize, market and sell our product candidates in the UK.  Brexit may also result in a reduction of funding to the EMA if the UK no longer makes financial contributions to European institutions, such as the EMA. If UK funding is so reduced, it could create delays in the EMA issuing regulatory approvals for our product candidates and, accordingly, have a material adverse effect on our business, financial condition, results or prospects.

If a natural or man-made disaster strikes our development or manufacturing facilities or otherwise affects our business, it could delay our progress developing and commercializing our drugs.

We currently rely on Ionis to manufacture our clinical supplies in a manufacturing facility located in Carlsbad, California and third party contract manufacturing organizations to manufacture active pharmaceutical ingredient and finished drug product for TEGSEDI. The facilities and the equipment required to develop and manufacture our drugs would be costly to replace and could require substantial lead time to repair or replace. Natural or man-made disasters, including, without limitation, earthquakes, floods, fires and acts of terrorism may harm these facilities. If a disaster affects these facilities, our and our partners' development and commercialization efforts would be delayed. Although we possess insurance for damage to our property and the disruption of our business from casualties, this insurance may not be sufficient to cover all of our potential losses and may not continue to be available to us on acceptable terms, or at all. In addition, a shutdown of the U.S. government, including the FDA could harm or delay our development and commercialization activities.

Our business and operations would suffer in the event of computer system failures.

We are dependent upon our own or third-party information technology systems, infrastructure and data, including mobile technologies, to operate our business. The multitude and complexity of our computer systems may make them vulnerable to service interruption or destruction, disruption of data integrity, malicious intrusion, or random attacks. Likewise, data privacy or security incidents or breaches by employees or others may pose a risk that sensitive data, including our intellectual property, trade secrets or personal information of our employees, patients, customers or other business partners may be exposed to unauthorized persons or to the public. Cyber-attacks are increasing in their frequency, sophistication and intensity. Cyber-attacks could include the deployment of

54

harmful malware, denial-of-service, social engineering and other means to affect service reliability and threaten data confidentiality, integrity and availability. Our business partners face similar risks and any security breach of their systems could adversely affect our security posture. A security breach or privacy violation that leads to disclosure or modification of or prevents access to patient information, including personally identifiable information or protected health information, could harm our reputation, compel us to comply with federal and/or state breach notification laws and foreign law equivalents, subject us to mandatory corrective action, require us to verify the correctness of database contents and otherwise subject us to litigation or other liability under laws and regulations that protect personal data, any of which could disrupt our business and/or result in increased costs or loss of revenue. Moreover, the prevalent use of mobile devices that access confidential information increases the risk of data security breaches, which could lead to the loss of confidential information, trade secrets or other intellectual property. While we have invested, and continue to invest, in the protection of our data and information technology infrastructure, there can be no assurance that our efforts will prevent service interruptions, or identify breaches in our systems, that could adversely affect our business and operations and/or result in the loss of critical or sensitive information, which could result in financial, legal, business or reputational harm to us. In addition, our liability insurance may not be sufficient in type or amount to cover us against claims related to security breaches, cyber-attacks and other related breaches .

Risks Related to Our Common Stock

We are an "emerging growth company" and as a result of the reduced disclosure and governance requirements applicable to emerging growth companies, our common stock may be less attractive to investors.

We are an "emerging growth company," as defined in the JOBS Act, and we may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not "emerging growth companies" including, but not limited to, the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved. We cannot predict if investors will find our common stock less attractive if we choose to rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stock and our stock price may be more volatile.

An active public trading market for our common stock may not be sustained.

Prior to the completion of our IPO in July 2017, no public market for our common stock existed. An active public trading market for our common stock may not be sustained. The lack of an active market may impair your ability to sell your shares at the time you wish to sell them or at a price that you consider reasonable. The lack of an active market may also reduce the fair value of your shares. An inactive market may also impair our ability to raise capital to continue to fund operations by selling shares. Additionally, as of February 20, 2019, Ionis owns approximately 75 percent of our outstanding common stock. Ionis intends to hold its shares of our common stock for the foreseeable future, which could reduce the public market for our stock.

The market price for our common stock may be volatile, which could contribute to the loss of your investment.

Fluctuations in the price of our common stock could contribute to the loss of all or part of your investment. There has been a public market for our common stock for a limited period of time. The trading price of our common stock is likely to be highly volatile and could be subject to wide fluctuations in response to various factors, some of which are beyond our control. Any of the factors listed below could have a material adverse effect on your investment in our common stock and our common stock may trade at prices significantly below your purchase price. In such circumstances the trading price of our common stock may not recover and may experience a further decline.

Factors affecting the trading price of our common stock may include:

55

56

Broad market and industry factors may materially harm the market price of our common stock irrespective of our operating performance. The stock market in general, and NASDAQ and the market for biotechnology companies in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of the particular companies affected. The trading prices and valuations of these stocks, and of ours, may not be predictable. A loss of investor confidence in the market for biotechnology or pharmaceutical stocks or the stocks of other companies which investors perceive to be similar to us, the opportunities in the biotechnology and pharmaceutical market or the stock market in general, could depress our stock price regardless of our business, prospects, financial conditions or results of operations.

Sales of a substantial number of shares of our common stock by our existing stockholders in the public market may cause our stock price to decline.

Sales of our common stock in the public market, or the perception that these sales may occur, could cause the market price of our common stock to decline. Novartis has agreed that it will not sell any of its shares until the earlier of January 5, 2020 or six months after we stop developing a drug under our agreement with Novartis. Thereafter, Novartis may only sell a limited number of shares each day. In addition, as of February 20, 2019 Ionis owns 67,383,965 shares, or approximately 75 percent, of our common stock. While the shares of common stock held by Ionis are eligible for sale in the public market, any sales by Ionis will be subject to volume limitations under Rule 144 under the Securities Act of 1933, as amended, or the Securities Act. In addition, 18,500,000 shares of common stock that are either subject to outstanding options or reserved for future issuance under our employee benefit plans are eligible for sale in the public market to the extent permitted by the provisions of various vesting schedules, the lock-up agreements and Rule 144 and Rule 701 under the Securities Act. To the extent the holders of these shares sell them into the market or our stockholders believe these sales might occur, the market price of our common stock could decline.

We cannot predict with certainty whether or when Ionis will sell a substantial number of shares of our common stock. Ionis' sale of a substantial number of shares, or a perception that such sales could occur, could significantly reduce the market price of our common stock.

We do not expect to pay any cash dividends for the foreseeable future.

You should not rely on an investment in our common stock to provide dividend income. We do not anticipate that we will pay any cash dividends to holders of our common stock in the foreseeable future. Instead, we plan to retain any earnings to maintain and expand our operations. Accordingly, investors must rely on sales of their common stock after price appreciation, which may never occur, as the only way to realize any return on their investment. As a result, investors seeking cash dividends should not purchase our common stock.

Changes in tax laws, regulations and treaties could affect our future taxable income.

A change in tax laws, treaties or regulations, or their interpretation, of any country in which we operate could materially affect us.  For Example, on December 22, 2017, the United States enacted H.R.1., known as the Tax Cuts and Jobs Act, which represented a substantial change to tax laws in the United States, but which did not have a material impact on our financial statements because we maintain a valuation allowance on all our net operating losses and other deferred tax assets.  However, any future changes in tax laws in any U.S. or non-U.S jurisdictions could have a material effect on our business.

We could be subject to additional tax liabilities.

We are subject to U.S. federal, state, local and sales taxes in the United States and foreign income taxes, withholding taxes and transaction taxes in foreign jurisdictions. Significant judgment is required in evaluating our tax positions and our worldwide provision for taxes. During the ordinary course of business, there are many activities and transactions for which the ultimate tax determination is uncertain. In addition, our tax obligations and effective tax rates could be adversely affected by changes in the relevant tax, accounting and other laws, regulations, principles and interpretations, including those relating to income tax nexus, by recognizing tax losses or lower than anticipated earnings in jurisdictions where we have lower statutory rates and higher than anticipated earnings in jurisdictions where we have higher statutory rates, by changes in foreign currency exchange rates, or by changes in the valuation of our deferred tax assets and liabilities. We may be audited in various jurisdictions, and such jurisdictions may assess additional taxes, sales taxes and value-added taxes against us. Although we believe our tax estimates are reasonable, the final determination of any tax audits or litigation could be materially different from our historical tax provisions and accruals, which could have a material adverse effect on our operating results or cash flows in the period for which a determination is made.

57

We could be subject to securities class action litigation.

In the past, securities class action litigation has often been brought against a company following a decline in the market price of its securities. This risk is especially relevant for us because biotechnology companies have experienced significant stock price volatility in recent years. If we face such litigation, it could result in substantial costs and a diversion of management's attention and resources, which could harm our business.

Provisions in our amended and restated certificate of incorporation, our amended and restated bylaws and Delaware law may have anti-takeover effects that could discourage an acquisition of us by others, even if an acquisition would be beneficial to our stockholders, and may prevent attempts by our stockholders to replace or remove our current management.

Our amended and restated certificate of incorporation, amended and restated bylaws and Delaware law contain provisions that may have the effect of delaying or preventing a change in control of us or changes in our management. Our amended and restated certificate of incorporation and bylaws include provisions that:

These provisions, alone or together, could delay or prevent hostile takeovers and changes in control or changes in our management. Further, Novartis has agreed that until Novartis holds less than 7.5% of our outstanding common stock, Novartis will vote the Novartis Private Placement Shares consistent with the recommendation of our board of directors. Although Novartis has retained the right to vote the Novartis Private Placement Shares in its sole discretion in connection with certain enumerated matters, including any transaction which would result in our change of control, our agreement with Novartis may nevertheless delay or prevent changes in our management or board of directors.

In addition, because we are incorporated in the State of Delaware, we are governed by the provisions of Section 203 of the Delaware General Corporation Law, which limits the ability of stockholders owning in excess of 15% of our outstanding voting stock to merge or combine with us.

Any provision of our amended and restated certificate of incorporation or amended and restated bylaws or Delaware law that has the effect of delaying or deterring a change in control could limit your opportunity to receive a premium for your shares of our common stock, and could also affect the price that some investors are willing to pay for our common stock.

Our bylaws designate the Court of Chancery of the State of Delaware and federal court within the State of Delaware as the exclusive forum for certain types of actions and proceedings that our stockholders may initiate, which could limit our stockholders' ability to obtain a favorable judicial forum for disputes with us or our directors, officers or employees.

58

Our bylaws provide that, subject to limited exceptions, the Court of Chancery of the State of Delaware and federal court within the State of Delaware will be exclusive forums for any:

Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and to have consented to the provisions of our bylaws described above. This choice of forum provision may limit a stockholder's ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers or other employees, which may discourage such lawsuits against us and our directors, officers and employees. Alternatively, if a court were to find these provisions of our amended and restated certificate of incorporation inapplicable to, or unenforceable in respect of, one or more of the specified types of actions or proceedings, we may incur additional costs associated with resolving such matters in other jurisdictions, which could adversely affect our business and financial condition.