Early onset calpainopathy with normal non-functional calpain 3 level

Abstract

Limb girdle muscular dystrophy 2A (LGMD2A), caused by calpain 3 deficiency, is currently diagnosed through the immunodetection of muscle protein by Western blot (WB) analysis . However, WB may provide normal results in patients with LGMD2A. The case of a female (3y 6mo of age) is described. She was found to be affected by asymptomatic hypercreatine-kinaesaemia during routine biochemical analysis at 10 months of age and had developed myopathic signs at the last neurological assessment. The WB of muscle biopsy performed at 28 months of age showed a normal quantity and pattern of bands for calpain 3. Despite this finding, on molecular analysis she was found to be a compound heterozygote for two mutations of the calpain 3 (CAPN3) gene (R110X and G222R). Autocatalytic activity assay showed a loss of function of calpain 3. This is the first genetically confirmed case of very early onset calpainopathy with a normal amount of protein at WB. Molecular analysis is also suggested in very young patients with normal WB.