Considering the marked differences in allele frequency that we observed between ethnic groups for the GAD2 SNPs (the −243 A>G and +61450 C>A SNPs in particular), as well as the known differences in the prevalence of class III obesity between Caucasian Americans and African Americans [31], it is plausible that a small difference in ancestry between cases and controls could lead to spurious claims of association. The gene discussed is GAD2; the disease is obesity due to melanocortin 4 receptor deficiency.