Until recently, only a few genomic disorders other than PWS were known to contribute to increased risk of obesity, including the known microdeletion syndromes 1p36 (OMIM #607872), 2q37 (OMIM #600430), 6q16 (SIM1 gene), 9q34 (OMIM #610253; EHMT1 gene), 11p14.1 (OMIM #612469), and 17p11.2 (OMIM #182290; RAI1 gene). This evidence concerns the gene SIM1 and obesity due to melanocortin 4 receptor deficiency.