We have investigated the muscle biopsies of 8 patients with myotonia congenita. There were
2 families with autosomal recessive inheritance (5 cases), 1 with autosomal dominant
inheritance, and 2 sporadic cases. Mild abnormalities were seen with routine pathological
preparations which were nondiagnostic. Histochemical studies of fiber subtypes
demonstrated a complete absence of Type 2B muscle fibers in all of our patients regardless
of the type of inheritance. This is the first report of an entity in which there is a consistent …