On Feb. 25, 2021, the U.S. Food and Drug Administration (FDA) granted approval to Sarepta Therapeutics for Amondys 45 (casimersen) injection for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 45 skipping (Exons are pieces of DNA that provide information for making proteins in a person’s genome).

The agency approved Amondys 45 based on an increase in dystrophin (a protein that helps keep muscle cells intact) production in skeletal muscle observed in patients treated with the therapy. This was the first FDA-approved targeted treatment for patients with this type of mutation. Approximately 8% of patients with DMD have a mutation that is amenable to exon 45 skipping.

DMD is a rare genetic disorder characterized by progressive muscle deterioration and weakness. It is the most common type of muscular dystrophy. DMD is caused by mutations in the DMD gene that results in an absence of dystrophin, a protein found in muscle fiber. The first symptoms are usually seen between three and five years of age and worsen over time. DMD occurs in approximately one out of every 3,600 male infants worldwide; in rare cases, it can affect females.