Duchenne muscular dystrophy (DMD) is caused by pathogenic sequence variants occurring in the DMD gene which lead to the loss of the dystrophin protein, a molecular ‘shock absorber’ that protects muscle from contraction-induced injury. The large size of the dystrophin open reading frame precludes delivery of the full-length protein using a single adeno-associated virus (AAV) vector, which led to the development of internally-deleted dystrophin minigenes encoding partially-functional dystrophin. Indeed, five such microdystrophin therapies have been assessed in various clinical programmes. In 2023, Elevidys (Sarepta Therapeutics) received accelerated approval based on levels of dystrophin as a surrogate biomarker. In 2024, it received full approval despite unclear efficacy (i.e. not meeting primary or secondary outcomes in a phase 3 trial). Additionally, in 2025, two DMD individuals treated with Elevidys died after acute liver failure. A separate microdystrophin therapy, PF-06939926 (Pfizer) was discontinued for both efficacy and safety reasons (including the deaths of two clinical trial participants). Solid Biosciences, Genethon, REGENXBIO, and Insmed continue to develop microdystrophin therapies differing in transgene structure, promoter sequences, and AAV serotype. Here we describe recent progress in AAV-microdystrophin therapeutics development, and discuss the challenges facing such approaches, including pre-existing anti-capsid immunity, anti-transgene immunity, the unknown functionality of microdystrophin transgenes, transduction of muscle stem cells, and long-term transgene persistence.
