The delivery of truncated ‘mini-dystrophin’ transgenes to patient cells5, 6, exon-skipping of defective dystrophin exons7–9 and gene-editing of defective DMD genomes10–13 have all shown promise in restoring partial protein expression, however, in each case the expectation is that at best the patient phenotype could be that of a less severe form of muscular dystrophy, owing to low levels of dystrophin restoration combined with a lack of functional domains in the internally deleted dystrophin products14. This evidence concerns the gene DMD and muscular dystrophy.