Alterations in Dysf pre-mRNA splicing incidentally created three 40aKO lines expressing varying levels of dysferlin (without residues encoded by exon 40a), allowing us to simultaneously evaluate the role of exon 40a and hypomorphic levels of the canonical dysferlin isoform (NM_001077694.2) on the muscle lipidome, proteome, membrane repair and development of a muscular dystrophy. The gene discussed is DYSF; the disease is muscular dystrophy.