Clinical progression of X-linked muscular dystrophy in two German Shorthaired Pointers

Abstract

2 full-sibling male German Shorthaired Pointer (GSHP) puppies (dogs 1 and 2) with X-linked muscular dystrophy and deletion of the dystrophin gene (gene symbol, DMD) each had poor growth, skeletal muscle atrophy, pelvic limb weakness, episodic collapse, and episodes of coughing. Initial examination revealed stunted growth, brachygnathism, trismus, and diffuse neuromuscular signs in each puppy; clinical signs were more severe in dog 2 than in dog 1. Immunohistochemical analysis revealed a lack of dystrophin protein in both dogs. During the next 3 years, each dog developed hyperinflation of the lungs, hypertrophy of the cervical musculature, and hypertrophy of the lateral head of the triceps brachii muscle. Monitoring and supportive care were provided at follow-up visits during an approximately 7-year period. No other specific treatment was provided. Neuromuscular signs in both dogs remained stable after 3 years of age, with dog 2 consistently more severely affected than dog 1. The dogs had multiple episodes of aspiration pneumonia; dogs 1 and 2 were euthanatized at 84 and 93 months of age, respectively. The clinical course of disease in these dogs was monitored for a longer period than has been monitored in previous reports of dystrophin-deficient dogs. The clinical progression of muscular dystrophy in the 2 GSHPs was compared with that for other breeds and species with dystrophin-deficient conditions, and the potential basis for the phenotypic variation observed between these littermates, along with potential therapeutic ramifications for dogs and humans, was evaluated.