Limb-girdle muscular dystrophy (LGMD) is a purely descriptive term, generally reserved for childhood- or adult-onset muscular dystrophies that are distinct from the much more common X-linked dystrophinopathies. LGMDs are typically nonsyndromic, with clinical involvement typically limited to skeletal muscle. Individuals with LGMD generally show weakness and wasting restricted to the limb musculature, proximal greater than distal, and muscle degeneration/regeneration on muscle biopsy. Most individuals with LGMD show relative sparing of the bulbar muscles, although exceptions occur, depending on the genetic subtype. Onset, progression, and distribution of the weakness and wasting vary considerably among individuals and genetic subtypes.
The limb-girdle muscular dystrophies typically show degeneration/regeneration (dystrophic changes) on muscle biopsy, which is usually associated with elevated serum creatine kinase concentration. For any male or female suspected of having limb-girdle muscular dystrophy, it is necessary to first rule out an X-linked dystrophinopathy. Biochemical testing (i.e., protein testing by immunostaining or immunblotting) performed on a muscle biopsy can establish the diagnosis of the following LGMD types: sarcoglycanopathy, calpainopathy, dysferlinopathy, and O-linked glycosylation defects (also known as dystroglycanopathy). In some cases, demonstration of complete or partial deficiencies for any particular protein can then be followed by mutation studies of the corresponding gene. Mutations in a number of genes have been associated with types of LGMD.
The term LGMD1 (including, e.g., LGMD1A, LGMD1B) refers to genetic types showing dominant inheritance, whereas LGMD2 refers to types with autosomal recessive inheritance. Mutations at more than 50 loci have been reported, making accurate diagnosis and genetic counseling a challenge. In most instances, the proband represents a simplex case, and the families can be counseled for recurrence risks associated with rare autosomal recessive conditions, which leaves a "significant" risk only for the sibs of the proband. If the causative mutation(s) have been identified in the family, prenatal testing for pregnancies at increased risk is possible through laboratories offering either testing for the gene of interest or custom testing.