FTO and obesity due to melanocortin 4 receptor deficiency: For example, in genome-wide association studies (GWAS), the rs9939609 SNP in the fat-mass-and-obesity-associated (FTO) gene has been reported to account for a modest, but a statistically significant, increase of 0.4 kg/m2 body mass index (BMI) units for each risk allele (A)7.