Indeed, recent studies have demonstrated that only the peripheral and not the intracerebroventricular administration of INSL5 induces an increase in appetite leading to obesity in mice, although data published so far on the expression of the INSL5 receptor RXFP4 in the hypothalamus have shown contrasting results [8,9]. The gene discussed is INSL5; the disease is obesity due to melanocortin 4 receptor deficiency.