Limb-Girdle Muscular Dystrophy Type 1B

Abstract

Limb-girdle muscular dystrophy type 1B is characterized by progressive limb-girdle weakness (affecting the pelvic before shoulder girdle), mild joint contractures, atrioventricular cardiac conduction disturbances, and dilated cardiomyopathy. The disease is due to mutations in the LMNA gene, encoding lamins A/C (Tables 6.1 and 6.2). Lamins are a major component of the nuclear envelope, separating the nucleoplasm from the rest of the cell. They are composed of an inner and outer nuclear membrane joined at nuclear pores and a nuclear lamina. Lamins A and C are the predominant forms and result from an alternatively splicing event. There is considerable clinical variability both between and within families with mutations in the LMNA gene. The different clinical forms, which are now often referred to as laminopathies, include the autosomal dominant form of Emery-Dreifuss muscular dystrophy type 2 and the allelic LGMD1B, familial partial lipodystrophy, axonal neuropathy (CMT2B1), mandibulo-sacral disease, premature ageing (progeria), and restrictive dermopathy.