Résumé :
|
Communication n° 133. INTRODUCTION : 1. Chloride channel (ClC-1) myotonia congenita in miniature schnauzer dogs has a delay in skeletal muscle relaxation following stimulation, diffuse skeletal muscle hypertrophy, stridor, and a stiff gait that improves with exercise. 2. Portuguese water dogs (PWD) with a novel juvenile dilated cardiomyopathy (JDCM) die suddenly at 13 (+/- 7.3) weeks of age (range, 2-32 weeks) due to congestive heart failure without previous signs or with clinical signs of congestive heart failure 1-5 days before death. Both genetic diseases are maintained in the animal colony of the Penn Veterinary School. OBJECTIVE: To further characterize two inherited myopathies in dogs. METHODS : 1. Seven homozygotes and four heterozygotes miniature schnauzers underwent quantitative electromyography. The dogs were anesthetized and measurements were recorded from the thoracic interosseous, pelvic interosseous, and cranial tibial muscles. 2. A normal non-PWD was outcrossed to a presumed heterozygous male PWD, and 3 female offspring were raised and bred to another presumed heterozygote male. The offspring were evaluated for juvenile dilated cardiomyopathy. RESULTS : 1. Heterozygous chloride channel deficient dogs had abnormal spontaneous activity (myotonic discharges) on electromyography. However, the mean duration of the myotonic discharge was significantly less for heterozygous compared to homozygotes. 2. In evaluating the PWD F1 backcrosses, one female produced 14 normal, and no affected pups. A second female produced 22 normal and no affected pups. The third produced 21 pups, 6 of which were affected. CONCLUSIONS : 1. Miniature schnauzer dogs heterozygous for myotonic myopathy showed the presence of myotonic discharges on needle electromyography, which is also the case in human heterozygous carriers of recessive myotonia congenita. However, the myotonic discharges were shorter in heterozygotes than in homozygotes. 2. JDCM in PWD is inherited as an autosomal recessive trait.
|