The summer has been filled with debates about the safety of Elevidys, Sarepta’s gene therapy for Duchenne muscular dystrophy. Four prominent researchers are now raising a fundamental question about its efficacy: How much gene does the gene therapy actually deliver?
In principle, the question should be settled. Since its first trial in 2017, Sarepta has taken muscle biopsies from participants and measured how much microdystrophin— a mini version of the gene broken in Duchenne — is present. (The gene has to be miniaturized to fit inside the virus that delivers it to cells.)
On average, Sarepta has said, patients produce roughly 35% microdystrophin, meaning their muscle cells have about a third as much of this miniature protein as healthy humans have of the full-length protein. The number was a key part of obtaining the drug’s initial accelerated approval in 2023 for 4- and 5-year-olds and its broader approval the following year.
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