[Congenital neuromuscular disease with uniform type 1 fibers : a case report].

A 3-year-old boy was seen because of delayed developmental milestones, waddling gait, nonprogressive proximal muscle weakness and hyporeflexia. Serum creatine kinase levels were normal and EMG was non-diagnostic. Muscle biopsy revealed complete absence of type 2 A and 2 B fibers in addition to a moderate variation in fiber size. Diagnostic findings for congenital nonprogressive myopathies were not present such as nemaline bodies, cores, targetoid structure, central nuclei or selective type 1 fiber atrophy. This was the first case of a distinct form of non-progressive congenital myopathy, "congenital neuromuscular disease (myopathy) with uniform type 1 fibers", accompanied with mental retardation in Japan.