Eteplirsen was FDA approved for a subset of patients with DMD who have out-of-frame mutations on exon 51 of the dystrophin gene. Patients who have in-frame mutations of the dystrophin gene usually retain partial function of the dystrophin protein and will present with Becker muscular dystrophy. Eteplirsen is complementary to a portion of exon 51 which causes the removal of exon 51 from the dystrophin mRNA prior to transcription, leading to a partially effective dystrophin protein.