Association of a novel dystrophin (DMD) genetic nonsense variant in a cat with X-linked muscular dystrophy with a mild clinical course.

X-linked muscular dystrophy in cats (FXMD) is an uncommon disease, with few reports describing its pathogenic genetic variants. A 9-year-old castrated male domestic shorthair cat was presented with persistent muscle swelling and breathing difficulty from 3 years of age. Serum activity of alanine aminotransferase, aspartate transaminase, and creatine kinase were abnormally high. Physical and neurological examinations showed muscle swelling in the neck and proximal limb, slow gait, and occasional breathing difficulties. Electromyography showed pseudomyotonic discharges and complex repetitive discharges with a "dive-bomber" sound. Histopathology revealed muscle necrosis and regeneration. Whole-genome sequencing identified a novel and unique hemizygous nonsense genetic variant, c.8333G > A in dystrophin (DMD), potentially causing a premature termination codon (p.Trp2778Ter). Based on a combination of clinical and histological findings and the presence of the DMD nonsense genetic variant, this case was considered FXMD, which showed mild clinical signs and long-term survival, even though immunohistochemical characterization was lacking.