Analysis of calpain-3 protein in muscle biopsies of different muscular dystrophies from India.

Background & objectives: Calpain-3, a Ca2+-dependent protease has been implicated in the pathology of neuromuscular disorders (NMDs). The current study aimed to analyze calpain-3 expression in cases diagnosed as muscular dystrophy from the Indian population. Methods: Calpain-3 Western blot analysis in muscle biopsies of immunohistochemically confirmed cases of Duchenne muscular dystrophy (DMD) (n=10), dysferlinopathy (n=30) and sarcoglycanopathy (n=8) was carried out. Calpain-3 Western blotting was also used in a blinded study to identify cases of calpain-3 deficiency in 28 NMD patients with potential muscular dystrophy. Results: Calpain-3 appeared as a full length 94 kDa band with an autolytic product (~60 kDa) on Western blots with antibody NCL-CALP-12A2 (Ab-2). Eight of the 10 DMD samples showed absence of 94 kDa band but presence of 60 kDa band while one case of sarcoglycanopathy showed absence of both. Twenty one of the 30 dysferlinopathy samples showed both bands while six showed only the 60 kDa band and three showed absence of both. In the blinded study, five NMD cases with potential muscular dystrophy that showed complete absence of both bands in retrospect exhibited clinical features of limb girdle muscular dystrophy 2A (LGMD2A). Interpretation & conclusions: While the study revealed a consistent pattern of calpain-3 in DMD, one sarcoglycanopathy and three dysferlinopathy samples exhibited secondary reduction in calpain-3. It was recognized that both calpain-3 bands should be considered to confirm calpain deficiency. Further, western blot offers an economical and fast preliminary screening method for LGMD2A especially in cases of complete absence of calpain-3 prior to conclusive diagnosis by genetic testing.