Targeted DUX4 base editing improves muscle function in an iPSC-derived model of childhood-onset FSHD

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common dominant muscular dystrophies and remains without an approved disease modifying therapy. Caused by the aberrant expression of the cytotoxic gene DUX4, FSHD is typically diagnosed in adulthood, however clinical onset in children (<18 years of age) is often associated with a more severe and rapid disease. While clinical trials are underway, a lack of human-specific pre-clinical models limit effective testing of potential therapies, particularly in children. To fill this gap, we describe here the development of induced pluripotent stem cell-derived 2-and 3-dimensional skeletal muscle models of children with clinically defined mild, moderate, and severe FSHD. These iPSC-derived muscle models replicate key features of FSHD, including aberrant DUX4 mRNA expression, muscle atrophy, and weakness, which correlate with the individuals specific disease severity. Next, we assessed the efficacy of adenine base editing (ABE) as a potential gene therapy approach to treat FSHD. DUX4-targeted ABE reduced DUX4 mRNA expression, improved muscle area and force generation in the most severe individual. Together this work supports the use of iPSC-derived skeletal muscle models as a less invasive method to study childhood-onset FSHD and establishes targeted DUX4 gene editing therapies as a potential treatment approach.