Genetic basis of Duchenne Muscular Dystrophy in Pembroke Welsh Corgis - is caused by an intronic insertion of a Long Interspersed Nuclear Element-1 (LINE-1, 4.8Kb) in intron 13 of the DMD gene. The DMD gene, located on the X chromosome, encodes dystrophin, a crucial protein for muscle cell membrane stability. This insertion leads to the introduction of a premature stop codon via abnormal exon inclusion, resulting in the absence of functional dystrophin protein. The mutation is inherited in an X-linked recessive manner, meaning males with the mutation are affected, while females are typically carriers.
Pathophysiology - Affected dogs show progressive loss of muscle mass and strength due to dystrophin deficiency, leading to muscle fiber degeneration and fibrosis. Clinical signs include feeding difficulties, delayed growth, muscle wasting, a short-stride shuffling gait, drooling, exercise intolerance, and difficulty walking. Immunostaining of muscle biopsies shows absence of dystrophin and compensatory upregulation of utrophin, a dystrophin homolog. Histopathology reveals muscle fiber size variation, necrosis, calcification, inflammation, and cardiac muscle degeneration.
Complications - Affected males experience progressive muscle wasting with severe mobility impairment by a few months of age. The disease is ultimately fatal with no current cure. Cardiac muscle degeneration can lead to heart failure as the disease progresses.
Why This Matters to Breeders and Vets - The Pembroke Welsh Corgi DMD model closely resembles human Duchenne muscular dystrophy in clinical and molecular features, making it valuable for studying disease pathogenesis and therapeutic approaches. Effects of carrier females can be mild but detectable as myopathy in some cases due to random X inactivation. Genetic testing is important for breeders to prevent propagation of this lethal disorder.