Childhood acid maltase deficiency. A clinical, biochemical, and morphologic study of three patients.

Three children, including two siblings and a patient with sporadic glycogenosis type II (childhood form of acid maltase deficiency [AMD] ), were studied clinically, biochemically, and morphologically. In addition to a delay in developmental milestones and mild generalized muscle weakness, nasal vocalization and an electromyographic finding of abnormal insertion voltage, followed by pseudomyotonic discharge, were assumed to be characteristic diagnostic findings for the childhood form of AMD. Since the neutral maltase activity was highest in the muscle biopsy specimen from the patient with the least severe weakness, the enzyme may play a role in reducing muscle involvement. Selective type 2A fiber atrophy and type 2B fiber deficiency in the affected muscles were the common histochemical findings in this particular form of AMD.