The normal function of GJA1/Gja1 is in the myometrium is coordination of the contractions at the end of the pregnancy, and is under control of a steroid hormone Expression of GJA1 has been shown to be down regulated in mammary tumors, lung cancer and endometrial adenocarcinoma [18,26-29], as GJA1/Gja1 normally maintains cell differentiation and prevents transformation into cancer cells [11,16,17]. This evidence concerns the gene GJA1 and breast cancer.