Dystrophin is the longest gene in the human genome and is much too large to fit into the adeno-associated virus (AAV) vector commonly used to deliver gene therapies. Replacing even some working protein in muscle cells should reverse the disease, or at least halt its progression.īut developing that replacement has proved difficult. The disease affects boys almost exclusively, because they have only one copy of the X chromosome, where the dystrophin gene is located girls with a disease-causing variant have a backup copy. “It’s a way to get our foot in the door now and help kids.” Why has DMD been so challenging to treat?ĭMD seems like a straightforward target for gene therapy. “To have a big success like this is going to validate the technology quite a bit,” says Jeffrey Chamberlain, a neurologist at the University of Washington in Seattle who developed some of the technologies used by Sarepta. Still, some scientists hope that the approval will pave the way for more gene therapies. A Sarepta spokesperson declined to reveal the price tag until the drug is approved but says that it will be priced “below the value it will bring to patients”. Analysts predict that the one-time treatment will cost US$2 million. A press release from the company says that the agency is likely to approve it only for boys aged four and five, but might expand that range if an ongoing clinical trial shows that the drug’s efficacy is worth the risks associated with it. The decision date was delayed late in May after FDA officials and advisers raised concerns about the strength of Sarepta’s data so far SRP-9001 seems to have only a modest effect on muscle function, and only in some people. Gene therapy’s comeback: how scientists are trying to make it safer The accelerated approval would allow the drug to reach the market before large clinical trials have been completed, on the basis of evidence that the therapy allows boys to make an engineered form of dystrophin. It would be the 13th gene therapy that the FDA has approved since 2017, and the first to target a prevalent genetic disease in children. The therapy, known as SRP-9001, is made by Sarepta Therapeutics based in Cambridge, Massachusetts. Children with DMD can’t make a protein called dystrophin, resulting in progressive muscle degeneration and death in their twenties due to heart or respiratory failure. On 22 June, the US Food and Drug Administration will decide whether to grant a fast-track approval to the first gene therapy for Duchenne muscular dystrophy (DMD), a genetic disorder that affects around 1 in 3,500 boys. The road to gene therapies for genetic disorders has been long - and expensive - but the field could soon get some good news.
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