RETN and obesity due to melanocortin 4 receptor deficiency: Genetic variation at the RETN locus carries a risk of several diseases, including the metabolic syndrome and colon cancer 15, 16 and those with a functional RETN gene polymorphism at -420 (rs1862513) are at risk of developing type 2 diabetes 17, 18, and associated with obesity in Tunisian population 19.