While there is a clear association between obesity and subfertility, the subject is complicated by whether this association is due to elevated insulin levels impacting ovarian function (as many obese women have an increased prevalence of polycystic ovarian syndrome [PCOS]), or if obesity is wielding actual undesirable effects on the endometrium and ovulation. The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.