Résumé :
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Limb girdle muscular dystrophy (LGMD) type 2A is caused by mutation in the gene encoding for calpain-3 resulting in total or partial loss of protein. Diagnosis of LGMD2A, the most prevalent form of LGMD, is established by analyzing calpain-3 protein deficiency or CAPN3 gene mutation. We have already identified and reported a cohort of 75 patients of calpainopathy based on semi-quantitative protein analysis of calpain-3 and dysferlin. A combined evaluation of 249 muscle biopsies that underwent western blotting and immunohistochemistry for respective proteins, the distribution of different major immunophenotypes are 39.36% calpainopathy, 16.9% dysferlinopathy, and 5.2% sarcoglycanopathy. However in patients with clinically diagnosed LGMD alone, the incidence of these was 45%, 19.9% and 5.2% respectively. The high frequency of LGMD2A could have been contributed by inclusion of possible LGMD2I patients showing partial loss of calpain-3. Hence for accurate diagnosis and ruling out secondary calpain-3 protein deficiency, we carried out CAPN3 mutation analysis primarily in 26 patients as part of pilot study. Initialy exon 1, 2, 4, 5, 6, 7, 8, 10, 11, 13, 15, 18, 19, 20, 21 and 22 were included for sequencing as these encompass the majority of mutation in known population of Europe, South America, United States and Asia on the basis of available literature. Our preliminary study has showed few known and some novel mutations viz Ex1 c.96 T>C, Ex4 c.515 C>T, Ex10 c.1194-9A>G, Ex22 c.1729-1G>T. Our findings of mutation are much similar to European data. The biopsies of these patients displayed dystrophic pattern with presence of active fibre necrosis, regeneration and lobulated fibres to end stage muscle disease. Involvement of the posterior compartment of the thigh was observed in all genotypically confirmed patients. The clinical features of our patients were generally in sync with the other characteristics of LGMD2A patients described in most of the studies. However one patient clinically presenting as miyoshi distal myopathy and one with polymyositis has shown mutation in calpain-3 gene. Now we are expanding mutation screening to all 75 candidate patients of LGMD2A whereas including remaining exons. To authenticate our mutation data, genotyping of calpain-3 gene for all the exons in normal control is under process.
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