Congenital fiber type disproportion in an adult: a morphometric and microchemical study.

A 20-year-old man with marfanoid habitus had a history of congenital hypotonia and muscle weakness. Muscle biopsy showed extreme fiber type disproportion. There was total absence of Type 2B fibers. The severely hypertrophic Type 2A fibers showed twice the normal concentration of creatine phosphate at rest. These advanced morphometric, histochemical and biochemical changes may be interpreted as compensatory phenomena, which may explain the patient's pronounced functional improvement with advancing age.