We have identified six novel alleles of known deafness genes (Klhl18 [10, 11], S1pr2 [12, 57–59], Atp2b2 [24, 25, 31–36], Tbx1 [43, 44, 60, 61], Pcdh15 [62] and Espn [63]), two of which (Tbx1ttch (MDLY), Atp2b2Tkh (MEBJ), Table 1) are hypomorphs which may be useful for in-depth studies of the function of these genes. The gene discussed is PCDH15; the disease is deafness.