LEP and obesity due to melanocortin 4 receptor deficiency: However, changes in blood concentration or dysfunction in endocrine pathways of leptin, adiponectin, resistin and kisspeptin could lead to dysregulation of fertility [106]: therefore, chronic impairment of nutritional balance (undernutrition, obesity and diabetes) or alterations in leptin or kisspeptin pathways [107] are risk factors for hypogonadotropic hypogonadism and infertility [108,109].