UCP1 and obesity due to melanocortin 4 receptor deficiency: In line with these data we observed increased IRX3 expression in UCP1-negative adipocytes compared to UCP1-positive adipocytes, but we did not observe an association of IRX5 and UCP1 expression in adipocytes of children indicating that IRX3 might be the main mediator of obesity risk in FTO risk variant carriers in children.