ANPEP and obesity due to melanocortin 4 receptor deficiency: Reduced expression of AdipoR1 and AdipoR2 has been also observed in endometria of women with recurrent implantation failure compared with fertile women, suggesting an important role of APN signaling in uterine receptivity and its possible contribution to implantation failures and pregnancy loss in women with maternal metabolic conditions such as obesity and PCOS [32].Resistin- Resistin is a small cysteine-rich 94-amino acid polypeptide.