Myopathy with a Possible Recessive X-Linked Inheritance in a Litter of Irish Terriers

Five male Irish Terrier puppies had a stiff gait, difficulty in swallowing, dirty cheeks because of food residues, an enlarged tongue and atrophic muscles. At electromyographical examination high-frequency discharges suggestive of myotonia were present. The values for serum creatine-phosphokinase and aldolase were extremely high. Serum vitamin E values were normal. At necropsy the muscles were pale with yellowish white streaks. Histologically there was a patchy distribution of the lesions. Granular and floccular changes (Zenker's degeneration) with phagocytosis, giant cells and calcification were found. Histochemical changes were the same in all muscles investigated, but were not equally pronounced. In the muscle specimens with greatest change the distinction between type I and type II fibres was largely lost. Rounded hypertrophic fibres contained no glycogen, and most did not show activity of phosphorylase, dehydrogenases, and oxidases. Activity of glyccrol-3-phosphate oxidase and acid phosphatase was markedly increased. Abnormal mitochondria and unknown electron-dense bodies were found. The tubular system seemed to be reduced in some abnormal fibres. The disease is probably recessive X-linked.