Fast to slow change of myosin in nemaline myopathy: electrophoretic and immunologic evidence.

Muscle biopsies from two familial and one sporadic case with congenital nemaline myopathy and seven healthy family members were examined for myosin composition. Myosin was characterized with respect to light chain (LC) composition by one-dimensional and two-dimensional electrophoresis, and by immunologic methods (enzyme-linked immunosorbent assay [ELISA]), using specific antibody for rabbit fast myosin LCl (LC1F). Type I fiber predominance was associated with the substitution of a hybrid, predominantly "slow" to a virtually pure "slow" myosin LC pattern for the "mixed" pattern found with myosin of normal muscle. Muscle myosin from the relatives had apparently normal light chain composition.