Recently, one study focused on the androgen receptor mediated signaling and its interaction with corticosteroid action in an experimental model characterized by obesity, the male androgen receptor–null mutant (ARKO) mice.86 The authors found that the obesity state in these animals was determined by an increased corticosteroid state due to impairment of a negative feedback regulatory system. The gene discussed is AR; the disease is obesity due to melanocortin 4 receptor deficiency.