TPH1 and major depressive disorder: More novel AD risk candidates implicated by our study included rs2020942 (P = 0.01, OR = 1.81), a SNP tagging the variable number tandem repeat in the serotonin transporter gene, SLC6A4, most often associated with depression [43,44]; rs1799913 (P = 0.04, OR = 0.64) in TPH1, an established depression risk factor [45] that was recently associated with depression in AD [34]; rs4504469 (P = 0.04, OR = 0.60) in KIAA0319, which was associated with dyslexia [46]; and rs1320490 (P = 0.05, OR = 1.63) in CDC42BPA, previously associated with reading ability [47].