Limb-girdle muscular dystrophy (LGMD) is one of the nine types of inherited muscular dystrophies, characterized by weakness in the muscles in the top (proximal) part of the arms and legs — specifically the hips, thighs, and shoulders.
More than 30 different subtypes of LGMD have been identified, each caused by mutations in at least one of several genes that play an essential role in muscle structure and function.
Autosomal dominant LGMD
The autosomal dominant pattern is known as LGMD1. There are at least eight LGMD1 subtypes, designated as LMGD1A to 1H, each caused by a mutation in a different gene. For example, subtypes 1A, 1B, and 1C are caused by mutations in the genes encoding for myotilin, lamins A/C, and caveolin 3, respectively.
LMGD1 subtypes are caused by the inheritance of a single mutant copy of the gene in question, from either the mother or the father. Despite the presence of one normal copy, the individual manifests the disease symptoms because the mutant gene dominates over the normal copy.
Autosomal recessive LGMD
The autosomal recessive pattern is known as LGMD2, which has more than 20 different subtypes, designated as LGMD 2A to 2Z. In each of these LGMD2 subtypes, the individual must inherit two mutant copies of the gene in question — one from the father and the second from the mother — to develop the disease. If the individual carries only a single mutant copy of the gene, they do not manifest the disease symptoms because the normal copy of the gene can adequately supplement the function of the protein encoded by that gene.
The genes that are mutated in both LGMD1 and LGMD2 encode for proteins that play a role in the structure, integrity, contraction, cell-to-cell signaling, cell membrane repair, or protein quality maintenance in muscles.
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