June 23, 2022

Dear United States Duchenne Community,

Today Sarepta announced that the United States Food and Drug Administration (FDA) has placed a clinical hold on SRP-5051 (vesleteplirsen) following a serious adverse event of hypomagnesemia that was identified through lab tests as part of our monitoring plan. This means that dosing is paused and new patients may not be enrolled in Study SRP-5051-201 (MOMENTUM) in the United States until the hold is lifted. The FDA has requested information on all cases of hypomagnesemia, including a small number of non-serious cases, and to assess the adequacy of the risk mitigation and safety monitoring plan. Sarepta will respond to the agency with this information and proposed changes to the monitoring plan in the next few days.

Safety for all study participants is our top priority. The hypomagnesemia was transient and patients’ magnesium levels returned to normal following additional supplementation.

What is SRP-5051 (vesleteplirsen)? Vesleteplirsen is an investigational medicine, a peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) in development for people with Duchenne muscular dystrophy who are amenable to exon 51 skipping.

Which study does this study hold impact? The SRP-5051-201 study, otherwise known as MOMENTUM (NCT04004065) will pause dosing and enrollment in the United States during this hold. Evaluations needed for safety follow-up will continue.

Why is there a hold? Recently there was a serious adverse event of hypomagnesemia in the MOMENTUM study. FDA is requesting information on all cases of hypomagnesemia, including a small number of non-serious grade 2 cases, and to assess the adequacy of the risk mitigation and safety monitoring plan

What is hypomagnesemia? Hypomagnesemia means low magnesium. Symptoms of hypomagnesemia can vary in severity and type.

How are the participants who experienced this event of hypomagnesemia? All participants who experienced hypomagnesemia have received magnesium supplementation and their magnesium levels have returned to baseline.

Has hypomagnesemia been seen before in this study? Yes, hypomagnesemia was seen in Part A of the MOMENTUM study. Before Part B of the study started, Sarepta changed the protocol to include supplementation of magnesium and magnesium monitoring.

When will the study start back up? We will work to share information with FDA with the goal of resuming screening and dosing in the United States as quickly as possible.

How full is this study? MOMENTUM is a multi-country study. Globally, we have enrolled approximately half of the planned patients in Part B of MOMENTUM.

We have great respect for patients and families who participate in clinical studies and appreciate the level of your commitment to help move the science forward. In the next few days we will share with FDA the requested information and proposed changes to the monitoring plan.   

If you are taking part in this study and have questions, please direct them to your clinical study staff. If you are a member of the Duchenne community and have any questions about this communication, please contact Patient Affairs at: [email protected].

Thank you,

The Sarepta Patient Affairs Team