We disclosed the expression of five connexin isotypes by confirming the production of GJA1/Cx43, GJA3/Cx46 and GJB2/Cx26 [27], [31], [40]–[42] and detecting, for the first time, GJA6/Cx30 and GJB1/Cx32 both in the human pre-menopausal mammary gland and breast carcinomas. Here, GJB2 is linked to breast carcinoma.