[Limb girdle muscular dystrophies]

Abstract

Limb girdle muscular dystrophies (LGMDs) are a genetically heterogeneous group of primary myopathies involving progressive weakness and wasting of the muscles in the hip and shoulder girdles, with distal spread to the bulbar or respiratory musculature in rare cases. Depending on the mode of genetic transmission, six autosomal dominant forms (LGMD1A-F, 10-25%) and ten autosomal recessive forms (LGMD2A-J, 75-90%) are currently known. The prevalence of LGMDs is 0.8/100,000. These conditions are caused by mutations in genes encoding for myotilin (5q31, LGMD1A), lamin A/C (1q11-q21.2, LGMD1B), caveolin-3 (3p25, LGMD1C), unknown proteins (7q, LGMD1D, 6q23, LGMD1E, 7q32.1-32.2., LGMD1F), calpain-3 (15q15.1-21.1, LGMD2A), dysferlin (2p13.3-13.1, LGMD2B), gamma-sarcoglycan (13q12, LGMD2C), alpha-sarcoglycan, also known as adhalin (17q12-q21.3, LGMD2D), beta-sarcoglycan (4q12, LGMD2E), delta-sarcoglycan (5q33-q34, LGMD2F), telethonin (17q11-q12, LGMD2G), E3-ubiquitin ligase (9q31-q34.1, LGMD2H), fukutin-related protein (19q13.3, LGMD2I), and titin (2q31, LGMD2J). Cardiac involvement has been described for LGMD1B-E, LGMD2C-G, and LGMD2I. The time of onset varies between early childhood and middle age. There is no male or female preponderance. Disease progression and life expectancy vary widely, even among different members of the same family. The diagnosis is based primarily on DNA analysis. The history, clinical neurological examinations, blood chemistry investigations, electromyography, and muscle biopsy also provide information that is helpful for the diagnosis. No causal therapy is currently available.