GJB2 and breast cancer: Although it remains unknown whether other tissues or organs that commonly express Cx26 are also susceptible to developing tumors, a single patient presenting with KID syndrome also presented with a primary invasive sccirrhous ductal carcinoma of the breast suggesting that a loss-of-function mutant of Cx26 may also have contributed to the onset of a primary breast tumour in humans similar to our conditional Cx26 knockout mouse model of breast cancer [58].