In addition, mutations in genes involved in the insulin signaling cascade (insulin receptor, PI3-kinase and AKT) cause severe insulin resistance [2,23] as well as mutations and polimorphisms in genes that predispose to obesity (melanocortin-4 receptor, leptin receptor, peroxisome proliferator-activated receptor PPARg). The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.