[Limb-girdle muscular dystrophy; update].

Sixteen different forms of limb-girdle muscular dystrophies (LGMDs) have emerged from recent molecular genetic studies, six forms with a dominant trait and ten forms with a recessive trait. Among 1,420 Japanese patients with muscular dystrophy analyzed at NCNP, LGMD is the secondly largest category (19%) following dystrophinopathy (56%). Within LGMDs, the occurrence of LGMD2A (calpainopathy), LGMD2B (dysferlinopathy), and LGMD2C-F (sarcoglycanopathy) is 26%, 18%, and 6.6%, respectively, however, causative genes have not been specified in about 50% of the LGMD patients. LGMD2A patients show atrophy prominent in shoulder and pelvic girdle muscles without calf muscle hypertrophy, and abundant lobulated fibers in muscle biopsy. Four major mutations unique to the Japanese population, have been identified. Pathogenesis attributes to a loss of proteolytic activity of mutant calpain-3. Dysferlin, the defective protein in LGMD2B, is a ferlin family molecule possessing six C2 domains probably mediating the resealing mechanism of the damaged sarcolemma. Mutations in the dysferlin gene result in Miyoshi distal myopathy and distal anterior compartment myopathy other than LGMD2B. Among four sarcoglyconopathies, LGMD2D is the most common form, whereas LGMD2F has not yet been reported. In sarcoglycan-deficient skeletal muscle, matrix metalloproteinases may be involved in the beta-dystroglycan processing which underlies the pathogenesis of sarcoglycanopathy.