Characteristics of myosin in nemaline myopathy.

Electron-microscopic, morphometric, histochemical and biochemical studies were carried out on muscle biopsies from a patient with the characteristic clinical and pathological findings of nemaline myopathy. The mean fiber diameter was decreased, and the vastus lateralis muscle biopsy consisted exclusively of slow twitch (Type I) fibers. Quantitative biochemical investigations revealed significantly low calcium uptake and ATPase activity of the fragmented sarcoplasmic reticulum and decreased myosin ATPase activity. The electrophoretogram of myosin showed an abnormality in the light chain pattern which could not be explained by a disproportion of normal fiber types.