Following the identification of TCF7L2, previously unknown genetic variants in the fat mass and obesity-associated (FTO) gene on chromosome 16 were also linked to T2DM risk through an effect on BMI [62], such that the 16% of adults homozygous for the rs9939609 “risk” A allele were 3 kg heavier and had 1.7 fold increased risk of obesity relative to the homozygous non-risk allele carriers. Here, TCF7L2 is linked to obesity due to melanocortin 4 receptor deficiency.