Recessive forms of severe obesity were identified, caused by homozygous or compound heterozygous mutations in the following genes: LEP (leptin), LEPR (leptin receptor), BBS1 and BBS10 (Bardet–Biedl syndrome), and POMC (pro-opiomelanocortin). This evidence concerns the gene LEPR and obesity due to melanocortin 4 receptor deficiency.