Given an OR of 1.5 at a nominal P = 0.05 for genotype frequencies ranging from 0.15 to 0.30, the statistical power of our study to detect an association of GRM3 with schizophrenia, HD, and major depression was estimated at 70.0–86.7%, 76.5–91.5%, and 68.6–85.6%, respectively. This evidence concerns the gene GRM3 and major depressive disorder.