A dual CRISPR-Cas3 system could be used to induce multi-exon skipping to restore the open reading frame of the dystrophin gene, a new study has found. Duchenne muscular dystrophy, a severe degenerative muscle disorder, is caused by mutations in the dystrophin gene that disrupt its open reading frame, leading to the loss of functional dystrophin proteins. Researchers from Kyoto University have used CRISPR-Cas3 to induce a deletion of 340 kilobases that restores that reading frame, as they report in Stem Cell Reports. To generate a large deletion spanning exons 45 to 55 — a in-frame deletion here is associated with milder disease — they relied on a pair of inward-facing crRNAs. In HEK293T cell lines and in iPSCs, including patient-derived IPSCs, this approach could generate a large deletion with few off-target effects, the researchers report. "Our dual-Cas3 system might apply to future gene therapies once we're able to deliver the dual-Cas3 components in vivo to skeletal muscle tissues safely and efficiently," senior author Akitsu Hotta from Kyoto and the Takeda-CiRA Joint Program says in a statement. "The ability to induce several hundred kilobases of DNA deletion itself also has broad applicability for basic research when a large deletion is needed."