Tryptophan hydroxylase 2 (TPH2) catalyzes the rate-limiting step in the synthesis of serotonin, and TPH2 polymorphisms have been investigated for association with depression, suicidal behavior, bipolar disorder (Zhang et al. 2006) and ADHD (Banaschewski et al. 2010; Brookes et al. 2006). Manor et al. (2008) tested for association of TPH2 SNPs and acute therapeutic response in children diagnosed with ADHD, and identified an 8-SNP haplotype (rs1386488, rs2220330, rs1386495, rs1386494, rs6582720, rs1386492, rs4760814, rs1386497; C–G–C–A–A–G–A–C) that was significantly associated with better acute therapeutic response following methylphenidate treatment.
