Résumé :
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Communication n° 320 Introduction : Limb-girdle muscular dystrophy (LGMD) is a heterogeneous group of disorders. Genetically LGMDs are divided into seven autosomal dominant (LGMD1A-G) and ten autosomal recessive (LGMD2A-J) forms. LGMD2A (calpainopathy) is caused by mutations in calpain3 gene, CAPN3, which usually lead to calpain3 protein defects. More than 100 CAPN3 mutations have been described. LGMD2I is caused by mutations in FKRP gene, which typically shows secondary reduction of alpha-dystroglycan expression. Mutations in FKRP gene can also cause congenital muscular dystrophy (MDC1C). Objectives : To investigate the occurrence of CAPN3 and FKRP mutations and protein defects in Finnish LGMD patients. Methods : To characterize possible protein defects of LGMD patients, we performed immunohistochemistry and western blot analysis from muscle samples using several antibodies to proteins associated with muscular dystrophy. 32 patients were analysed, of whom 8 were not yet sequenced for CAPN3 gene mutations. CAPN3 and FKRP genes of 30 LGMD patients were analyzed by sequencing using DNA isolated from blood. Exons 1, 4, 5, 8, 10, 11, 15, 20 and 21 from CAPN3, and all the coding region of FKRP were sequenced. Results : Among 30 LGMD patients analysed by sequencing, CAPN3 and FKRP defects were found in 11 patients. We have identified two new FKRP gene mutations, Q77X in patient 1 and A321E in patient 2. Both occured together with the previously known L276I FKRP mutation in compound heterozygotes. In CAPN3 gene we found a new homozygous mutation T3N in patient 3 and a heterozygous mutation G234R in patient 4. Previously known CAPN3 mutation Y745X shown to occur in compound heterozygous state was now also found in homozygous state (in patient 5). Among all blotted patients, 12 showed calpain 3 protein defects. All three patients with CAPN3 mutations T3N, G234R and Y745X, showed severe decrease in calpain3 protein expression. These patients also showed secondary alteration in dystrophin protein expression on western blot with c-terminal antibody, whereas dystrophin was normal on sections. Conclusions : Defects in calpain 3 and in FKRP may occur with the same frequency in Finland as in other European countries. Although our material was limited, a few mutations might be specific to Nordic populations. Western blotting is well established for detecting primary and secondary protein defects.
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