Familial neuromuscular disease with type 1 fiber hypoplasia, tubular aggregates, cardiomyopathy, and myasthenic features.

Three sisters had autosomal recessive inheritance of a cardiomyopathy, and nonprogressive proximal muscle weakness and lordosis that began in childhood. Small type 1 fibers and tubular aggregates in both fiber types were found on muscle biopsy. In addition, myasthenic features were characterized by fatigability with moderate exercise, decremental response to repetitive nerve stimulation, and improved function with anticholinesterase drug therapy.