Limb-girdle Muscular Dystrophy

지대형 근이양증

Limb-girdle muscular dystrophy (LGMD) is a heterogeneous group of inherited muscle disorders caused by the mutations of different genes encoding muscle proteins. In the past, when the molecular diagnostic techniques were not available, the subtypes of muscular dystrophies were classified by the pattern of muscle weakness and the mode of inheritance, and LGMD had been considered as a 'waste basket' of muscular dystrophy because many unrelated heterogeneous cases with 'limb-girdle' weakness were put into the category of LGMD. With the advent of molecular genetics at the end of the last century, it has been known that there are many subtypes of LGMD caused by the mutation of different genes, and now, LGMD is classified according to the results of the linkage analysis and the genes or proteins affected. Only small proportion (probably less than 10%) of LGMD is dominantly inherited, and autosomal dominant LGMD (AD-LGMD) consists of six subtypes (LGMD1A to 1F) so far. In autosomal recessive LGMD (AR-LGMD), more than 10 subtypes (LGMD2A to 2J) have been linked and most of the causative genes have been identified. Among AR-LGMDs, LGMD2A (calpain 3 deficiency), 2B (dysferlin deficiency), and sarcoglycanopathy (LGMD2C-2F) are major subtypes. The defective proteins in LGMDs are components of nuclear envelope, cytosol, sarcomere, or sarcolemma, and seem to play a different role in the pathogenesis of muscular dystrophy. It is notable that many causative genes of LGMDs are also responsible for other categories of muscular dystrophy or diseases affecting other tissue. However, by which mechanism they produce such a broad phenotypic variability is still unknown. The identification of mutation in the relevant gene is confirmative for the diagnosis, and is essential for genetic counseling and antenatal diagnosis of LGMD. Because many different genes are responsible for LGMD, differentiation of subtypes using immunohistochemistry and western blotting is the essential step toward the detection of mutation. For the effective research and medical care of the patients with muscular dystrophy in Korea, a research center with a medical facility supported by the government seems to be needed.