Calpains are a family of cytosolic calcium activated cysteine proteases involved in a variety of cellular processes including apoptosis, cell division, modulation of integrin and cytoskeletal interactions, and synaptic plasticity. Calpain 12 was first described in the mouse, most strongly in the skin, and maps to mouse chromosome 7. Isoforms differ in the carboxyterminal ends, ending with aberrant domain III and lacking domain IV. Domains in the large subunit include the amino terminal domain I, the proteinase domain II, domain III, and the EF hand domain IV, making Calpain 12 most similar to calpains 1 and 2.