In September 2016, the US Food and Drug Administration (FDA) approved eteplirsen (Exondys 51), a new drug for Duchenne muscular dystrophy (DMD), overruling the recommendations of both its scientific staff and its external advisory committee. Duchenne muscular dystrophy is a progressive X-linked genetic disease caused by mutations in a gene that produces the protein dystrophin that helps stabilize muscle fibers. It is usually fatal by the third decade of life. No disease-modifying treatments are available.