Calpainopathy: how broad is the spectrum of clinical variability?

Five affected siblings were referred with a probable diagnosis of proximal adult-type spinal muscular atrophy (SMA) based on lower motor neuron signs (muscle weakness and atrophy, hypotony, hypoactive or absent reflexes, and fasciculations), normal or borderline serum creatine kinase levels, and a neurogenic pattern on electromyography, compatible with motor neuron disease, in one patient. No exon 7-8 deletion in the survival motor neuron (SMN) gene was found. Linkage analysis excluded the SMN and all known autosomal recessive limb girdle muscular dystrophy loci, with the exception of LGMD-2A. A homozygous R769Q mutation in the calpain-3 gene and absence of muscle calpain-3 protein confirmed a calpainopathy. This family suggests that the clinical spectrum of calpainopathy might be broader and that this diagnosis might be considered in patients with an atypical motor neuron disease.