As the GAD2 variant allele −243 G was in the 5′ region of the gene (the other two SNPs were located in intronic regions), displayed the strongest association with class III obesity in the case-control study, and was in linkage disequilibrium with the +61450 C>A and +83897 T>A SNPs, functional studies were performed to test its effects on transcription and nuclear protein binding. This evidence concerns the gene GAD2 and obesity due to melanocortin 4 receptor deficiency.