Beta-sarcoglycanopathy (LGMD 2E) in a Spanish family

Out of 10 autosomal recessive limb-girdle muscular dystrophies reported, 4 are caused by mutations in the genes encoding for sarcoglycans (alpha-, beta-, gamma- and delta-SG). Beta-sarcoglycanopathy (limb-girdle muscular dystrophy 2E) is a genetically heterogeneous disorder which usually presents a severe progressive clinical course. A complete immunohistochemical evaluation of the sarcoglycan complex should be carried out to direct the mutation analysis approach. The present report concerns a Spanish family with a genetically confirmed beta-sarcoglycanopathy. The patient, a 16-year-old female, offspring of a consanguineous marriage, developed a severe limb-girdle muscular dystrophy with a Duchenne-like phenotype. Muscle biopsy showed dystrophic changes and complete absence of the four sarcoglycans. Genetic analysis demonstrated homozygosis for the M100K missense mutation in exon 3, encoding for the proximal extracellular domain. The parents and one sister were found to be carriers. Missense mutations affecting this domain result in the instability of the entire sarcoglycan complex and lead to severe phenotypes as seen in non-sense mutations.