SLC6A4 and major depressive disorder: Methods: Polymorphisms in SLC6A4 (5-HTTLPR, rs25531, 5-HTTLPR-rs25531, and STin2 VNTR) and TPH2 (rs1843809, rs1386494, rs4570625, and rs34517220) were genotyped in 368 HIV+ children and adolescents (aged 5–17 years) with any internalizing mental disorder (depression, anxiety disorders, or posttraumatic stress disorder), and 368 age- and sex-matched controls, who were also HIV+.