AHR and major depressive disorder: To determine whether the DEFB1 and AHR SNPs that were identified during the GWAS for plasma KYN concentrations might be directly associated with severity of MDD symptoms, we determined associations of these SNPs with the severity of symptoms measured by both HAMD-17 and QIDS-C16 scores in the larger cohort of all 803 patients who were recruited to the Mayo-PGRN AMPS study14.