DMD and Duchenne muscular dystrophy: For DMD caused by exon 50 deletion, a CRISPR/Cas9-induced single cut at the exon 51 splice acceptor site skipped exon 51 or introduced an in-frame insertion.507,508 For DMD caused by a point mutation, 2 cuts at the flanking introns removed the nonsense exon with or without nearby exons.509–513 These studies all reported high efficiency in restoring dystrophin expression and skeletal and cardiac muscle function.