Recurrent exertional rhabdomyolysis and stunted growth

A boy with recurrent exertional rhabdomyolysis and stunted growth is described. Fetal movements were few and the boy was small for gestational age. He always experienced easy fatigability, and he noted bouts of pigmenturia associated with episodes of considerable malaise. The change in color of the urine was caused by myoglobin. An electromyogram was myopathic. CPK rose during 60 minutes mild exercise. Prolonged moderate exercise could not be performed. Histopathological examination of muscle biopsy revealed an increase in the number of 11C fibres (20%). Electronmicroscopy revealed the wavy outline of a number of fibres and hypertrophy of sarcoplasmic reticulum elements. No cause for the stunted growth could be detected.