Four new mouse models of Duchenne muscular dystrophy with clinically relevant exon deletions in the human DMD gene.

Variant-specific therapeutic approaches, such as exon skipping or gene editing, hold promise for the treatment of Duchenne muscular dystrophy (DMD). Translatability of preclinical studies investigating these approaches could greatly be improved through the use of humanized mouse models, as these allow preclinical testing of human-specific sequences. We developed four novel humanized mouse models of DMD with a deletion of exon 44, 45, 51 or 53 in the human DMD gene, in a mouse dystrophin-negative background (mdx mouse; exon 23 nonsense mutation). Our optimized prescreening pipeline allowed us to do so very efficiently with the CRISPR-Cas9 technology. We confirmed either complete lack of dystrophin or expression of trace levels, which led to development of muscle pathology consisting of muscle fiber degeneration and regeneration, inflammation and fibrosis in young adult mice. Intramuscular treatment with vivo-morpholinos targeting a flanking exon induced exon skipping in the DMD strains, which restored the disrupted open reading frame and, subsequently, dystrophin expression. This validates these models as valuable tools for preclinical studies investigating human sequence-specific therapeutic approaches for DMD.