α-Sarcoglycan Analysis in Cases with Limb-girdle Muscular Dystrophy

Sarcoglycans are components of the dystrophin-glycoprotein complex which confer a link between the extracellular matrix and the cytoskeleton. α-Sarcoglycan (α-SG), a 50-kDa glycoprotein, is closely associated with three other sarcoglycans and the α-SG gene is involved in an autosomal recessive type of limb-girdle muscular dystrophy (LG). From 232 patients with various neuromuscular diseases, including 122 cases of muscular dystrophy, nine cases were clinically identified with LG. PCR and digestion by restriction enzyme Nla IV revealed a C→T substitution at nt. 229 which has been reported as a mutation hot spot of the α-SG gene in one case. The mother of this case was shown to carry the same mutation heterozygously. In another LG case, α-SG was not expressed on muscle membrane in immunohistochemical analysis, however the mutation at the hot spot was not detected. Finally, two cases were diagnosed as sarcoglycanopathy. These cases showed the following characteristic features; normal motor development, more rapid progression, severe myalgia and greater impairment of the neck flexor muscle. Since sarcoglycanopathy is very rare, the cases should be selected by close clinical study and immunostaining, and DNA analysis of the mutation hot spot of the α-SG gene should be attempted