– Phase 2 Study will Evaluate the Safety and Efficacy of Lumasiran in Patients with Recurrent Kidney Stone Disease and Elevated Urinary Oxalate Levels –

Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), the leading RNAi therapeutics company, today announced that the company has initiated a global Phase 2 study to evaluate the safety and efficacy of lumasiran, an RNAi therapeutic targeting hydroxyacid oxidase 1 (HAO1) – the gene encoding glycolate oxidase (GO) – in patients with recurrent kidney stone disease and elevated urinary oxalate levels. Lumasiran is approved by the U.S. Food and Drug Administration (FDA) for the treatment of primary hyperoxaluria type 1 (PH1) to lower urinary oxalate levels in pediatric and adult patients and by the European Medicines Agency (EMA) for the treatment of PH1 in all age groups, in each region under the brand name OXLUMO^®.

“Recurrent kidney stone disease is a prevalent disease, associated with significant clinical burden, including pain, infection, hospitalizations, and an increased risk of developing chronic kidney disease and kidney failure. The majority of kidney stones in adults are formed from calcium oxalate crystals and are accompanied by elevated urinary oxalate,” said Jeroen Valkenburg, General Manager, Lumasiran program at Alnylam. “To that end, we believe the reductions in urinary oxalate due to silencing of hepatic HAO1 we see with lumasiran in patients with primary hyperoxaluria type 1 may potentially apply to other diseases characterized by oxalate overproduction, such as recurrent kidney stone disease, where despite standard of care, stones continue to recur. We look forward to testing this hypothesis in this Phase 2 study.”

About the Phase 2 Study in Patients with Recurrent Kidney Stone Disease

The Phase 2 trial is a randomized, double-blind, placebo-controlled study to evaluate the safety, efficacy, pharmacodynamics, and pharmacokinetics of lumasiran administered subcutaneously in patients with recurrent calcium oxalate kidney stone disease and elevated urinary oxalate levels. This global, multicenter trial is expected to enroll 120 adults with a documented diagnosis of recurrent calcium oxalate kidney stone disease, based on two or more stone events within five years prior to screening, and whose 24-hour urinary oxalate levels are greater than the upper limit of normal. Study participants will be randomized 1:1:1 to receive either placebo or lumasiran at 567 mg or 284 mg on Day 1, Month 3, and Month 9 of a 15-Month double-blind treatment period that includes a six-month primary analysis period followed by a nine-month treatment extension period. The primary endpoint of the Phase 2 study is the percent change in 24-hour urinary oxalate after six months of treatment. Key secondary endpoints include the percentage of patients who achieve a 20 percent or greater reduction in 24-hour urinary oxalate and percent change in urinary calcium oxalate supersaturation after six months of treatment. For more information on the Phase 2 study (NCT05161936), please visit clinicaltrials.gov, email clinicaltrials@alnylam.com or call 877-256-9526 in North America and +31 20 369 7861 in Europe.

About Lumasiran

Lumasiran is a subcutaneously administered RNAi therapeutic targeting hydroxyacid oxidase 1 (HAO1) in development for the treatment of advanced primary hyperoxaluria type 1 (PH1) and recurrent kidney stone disease. HAO1 encodes glycolate oxidase (GO). Thus, by silencing HAO1 and depleting the GO enzyme, lumasiran inhibits production of oxalate – the metabolite that directly contributes to the pathophysiology of PH1 and recurrent kidney stone disease. Lumasiran utilizes Alnylam's Enhanced Stabilization Chemistry (ESC)-GalNAc-conjugate technology, which enables subcutaneous dosing with increased potency and durability and a wide therapeutic index. Lumasiran has received regulatory approvals from the U.S. Food and Drug Administration (FDA) for the treatment of PH1 to lower urinary oxalate levels in pediatric and adult patients and from the European Medicines Agency (EMA) for the treatment of PH1 in all age groups under the brand name OXLUMO^®.

OXLUMO^® (lumasiran) INDICATION AND IMPORTANT SAFETY INFORMATION

Indication

OXLUMO is indicated for the treatment of primary hyperoxaluria type 1 (PH1) to lower urinary oxalate levels in pediatric and adult patients.

Important Safety Information

Adverse Reactions

The most common adverse reaction that occurred in patients treated with OXLUMO was injection site reaction (38%). Symptoms included erythema, pain, pruritus, and swelling.

Pregnancy and Lactation

No data are available on the use of OXLUMO in pregnant women. No data are available on the presence of OXLUMO in human milk or its effects on breastfed infants or milk production. Consider the developmental and health benefits of breastfeeding along with the mother’s clinical need for OXLUMO and any potential adverse effects on the breastfed child from OXLUMO or the underlying maternal condition.

For additional information about OXLUMO, please see the full U.S. Prescribing Information.

About Recurrent Kidney Stone Disease

It is estimated that one in eleven people will experience a kidney stone at some point in their lifetime. Approximately 80 percent of kidney stones in adults are formed from calcium oxalate crystals with up to 2.5 million Americans having recurrent calcium oxalate stone disease with elevated urinary oxalate. Kidney stones can cause painful urination and blood in the urine, flank pain, urinary tract infections, and can require hospitalizations and surgery for removal. They are associated with a greater risk of developing chronic kidney disease (CKD) and end stage kidney disease (ESKD). There are limited effective treatment options for recurrent kidney stone disease and despite best standard of care – including dietary and lifestyle changes, citrate supplementation, and thiazide diuretics – recurrent stones still occur.

About RNAi

RNAi (RNA interference) is a natural cellular process of gene silencing that represents one of the most promising and rapidly advancing frontiers in biology and drug development today. Its discovery has been heralded as “a major scientific breakthrough that happens once every decade or so,” and was recognized with the award of the 2006 Nobel Prize for Physiology or Medicine. By harnessing the natural biological process of RNAi occurring in our cells, a new class of medicines, known as RNAi therapeutics, is now a reality. Small interfering RNA (siRNA), the molecules that mediate RNAi and comprise Alnylam's RNAi therapeutic platform, function upstream of today’s medicines by potently silencing messenger RNA (mRNA) – the genetic precursors – that encode for disease-causing or disease pathway proteins, thus preventing them from being made. This is a revolutionary approach with the potential to transform the care of patients with genetic and other diseases.

About Alnylam Pharmaceuticals

Alnylam (Nasdaq: ALNY) is leading the translation of RNA interference (RNAi) into a whole new class of innovative medicines with the potential to transform the lives of people afflicted with rare genetic, cardio-metabolic, hepatic infectious, and central nervous system (CNS)/ocular diseases. Based on Nobel Prize-winning science, RNAi therapeutics represent a powerful, clinically validated approach for the treatment of a wide range of severe and debilitating diseases. Founded in 2002, Alnylam is delivering on a bold vision to turn scientific possibility into reality, with a robust RNAi therapeutics platform. Alnylam’s commercial RNAi therapeutic products are ONPATTRO^® (patisiran), GIVLAARI^® (givosiran), and OXLUMO^® (lumasiran), as well as Leqvio^® (inclisiran), which is being developed and commercialized by Alnylam’s partner Novartis. Alnylam has a deep pipeline of investigational medicines, including six product candidates that are in late-stage development. Alnylam is executing on its “Alnylam P⁵x25” strategy to deliver transformative medicines in both rare and common diseases benefiting patients around the world through sustainable innovation and exceptional financial performance, resulting in a leading biotech profile. Alnylam is headquartered in Cambridge, MA. For more information about our people, science and pipeline, please visit www.alnylam.com and engage with us on Twitter at @Alnylam, on LinkedIn, or on Instagram.

Alnylam Forward Looking Statements

Various statements in this release concerning Alnylam's future expectations, plans and prospects, including, without limitation, Alnylam’s views with respect to the safety and efficacy of lumasiran in patients with recurrent kidney stone disease, the potential of lumasiran to be effective in the treatment of other diseases characterized by oxalate overproduction, Alnylam’s aspiration to become a leading biotech company, and the planned achievement of its “Alnylam P⁵x25” strategy, constitute forward-looking statements for the purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. Actual results and future plans may differ materially from those indicated by these forward-looking statements as a result of various important risks, uncertainties and other factors, including, without limitation: the direct or indirect impact of the COVID-19 global pandemic or any future pandemic on Alnylam’s business, results of operations and financial condition and the effectiveness or timeliness of Alnylam’s efforts to mitigate the impact of the pandemic; the potential impact of the planned leadership transition at year end on Alnylam’s ability to attract and retain talent and to successfully execute on its “Alnylam P⁵x25” strategy; Alnylam's ability to discover and develop novel drug candidates and delivery approaches and successfully demonstrate the efficacy and safety of its product candidates; the pre-clinical and clinical results for its product candidates; actions or advice of regulatory agencies and Alnylam’s ability to obtain and maintain regulatory approval for its product candidates, as well as favorable pricing and reimbursement; successfully launching, marketing and selling its approved products globally; delays, interruptions or failures in the manufacture and supply of its product candidates or its marketed products; obtaining, maintaining and protecting intellectual property; Alnylam’s ability to successfully expand the indication for OXLUMO or ONPATTRO (and vutrisiran, if approved) in the future; Alnylam's ability to manage its growth and operating expenses through disciplined investment in operations and its ability to achieve a self-sustainable financial profile in the future without the need for future equity financing; Alnylam’s ability to maintain strategic business collaborations; Alnylam's dependence on third parties for the development and commercialization of certain products, including Novartis, Sanofi, Regeneron and Vir; the outcome of litigation; the potential impact of current and the risk of future government investigations; and unexpected expenditures; as well as those risks more fully discussed in the “Risk Factors” filed with Alnylam's most recent Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) and in its other SEC filings. In addition, any forward-looking statements represent Alnylam's views only as of today and should not be relied upon as representing its views as of any subsequent date. Alnylam explicitly disclaims any obligation, except to the extent required by law, to update any forward-looking statements.

This release discusses the use of a previously approved RNAi therapeutic in continued development and is not intended to convey conclusions about efficacy or safety as to these uses. There is no guarantee that the data described in this release will result in expanded use of this commercial product, will successfully complete clinical development or will gain health authority approval.

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