MUC1 and Infertility: In conclusion, it has been shown that the altered expression of MUC1 is associated with infertility problems, suggesting that in cases of reduced expression, the endometrium might be unable to direct the blastocyst to the implantation site or, in cases of increased expression, MUC1 carbohydrate chains might prevent the blastocyst from adhering to the endometrial surface.