THE ETIOLOGY and pathogenesis of childhood x-linked pseudohypertrophic muscular dystrophy ("Duchenne dystrophy") remains obscure, even though the histopathology and clinical picture were described by Duchenne1in 1868, and Erb2formalized the concept of a primary dystrophic disease of muscle in 1891. Meryon3in 1864 suggested that it may be "... an idiopathic disease of the muscle, dependent perhaps on defective nutrition." Recent emphasis has centered on multiple possibilities, including a metabolic defect intrinsic to the muscle fiber or muscle-fiber membrane,4-7a functional vascular abnormality,8-11an autoimmune process,12an abnormal circulating serum factor,13an endocrine abnormality,10,14,15and a primary defect involving connectivetissue proliferation.16 The earliest histological changes seen in minimally weak, or even clinically normal, muscles of patients with Duchenne muscular dystrophy aresmall fociofgroupedmuscle fibers undergoing necrosis or regeneration, all fibers of the group being in about the