Limb-girdle muscular dystrophy.

The limb-girdle muscular dystrophies (LGMDs) are a group of muscular dystrophies that share a similar clinical phenotype. Despite this clinical homogeneity, at least 15 different genetic forms of LGMD are now known. Some of these share pathogenetic mechanisms with other forms of muscular dystrophy, such as the sarcoglycanopathies (LGMD 2C-F) and the dystrophinopathies (Duchenne and Becker muscular dystrophy). Some are allelic with other forms of muscular dystrophy; LGMD 1B is allelic with autosomal dominant Emery-Dreifuss muscular dystrophy. Still others introduce totally unique pathogenetic mechanisms to the study of muscular dystrophy. For example, LGMD 2H appears to be due to mutations affecting the ubiquitin-proteasome pathway. A diagnostic approach is outlined based on clinical features, genetics, and commercially available testing.