The spontaneous mutant, Wriggle Mouse Sagami (wri), is thought to be a model of hereditary hearing losses in humans. Here we report that the plasma membrane Ca 2 + -ATPase type 2 (PMCA2) gene is mutated in the wri mouse. A G-to-A transition was detected in wri, changing Glu-to-Lys within a conserved transmembrane domain. Mutation of PMCA2 was previously reported in deafwaddler (dfw) mutants; however, the sites of the wri and dfw mutations differ. Immunohistochemical analysis demonstrated that PMCA2 labeling in stereocilia of the cochlea was absent in the wri mutant, suggesting that PMCA2 is crucially involved in the physiology of the auditory system.