Myoadenylate deaminase deficiency or not? Observations on two brothers with exercise-induced muscle pain

This paper describes 2 brothers with increasingly severe exercise-induced muscle pain and stiffness, beginning in adolescence. Histochemical studies showed that myoadenylate deaminase activity was absent in the propositus, but present in his younger brother. Biochemical examination of muscle homogenates confirmed these findings, with enzyme activity approximately 60% of the mean control value in the younger sibling. Red cell adenylate deaminase activity was normal in both cases. The possible relationship between the clinical and biochemical findings in these patients is discussed.