The importance of calpains' physiological roles in mammals is revealed by the various phenotypes caused by calpain deficiencies, including embryonic lethality (in Capn2- or Capns1-deficient mice) [7]–[10], muscular dystrophies (human/mouse CAPN3/Capn3) [11]–[13], gastropathy (mouse Capn8 and Capn9) [14], and vitreoretinopathy (human CAPN5) [15]. The gene discussed is CAPN3; the disease is vitreoretinal degeneration.