Calpains are a group of proteins that function as non-lysosomal intracellular calcium-dependent cysteine proteases. Structurally calpains are heterodimers made up of a large catalytic subunit and a smaller regulatory subunit. The CAPN3 gene encodes a muscle-specific large subunit of this protein that binds specifically with titin. Disruption of the CAPN3 enzymatic activity has been found to negatively affect muscle membrane repair and remodeling.
Mutations in this gene have been associated with Muscular Dystrophy, Limb-Girdle, Type 2A (LGMD2A), a progressive autosomal recessive disorder characterized by proximal muscle atrophy, scapular winging, calf pseudohypertrophy, and contractures.