For this study our aim was to detect all common variants in the genes PCLO, GRM7 and SLC6A4 in 50 control samples of the Dutch GAIN-MDD cohort and then genotype these variants for the full cohort, in order to test if we could identify a more likely causal variant than rs2522833 for MDD in this Dutch cohort. The gene discussed is SLC6A4; the disease is major depressive disorder.