To date, three non-synonymous TPH2 SNPs have been associated with psychiatric disorders in humans, which severely impair TPH2 enzymatic activity by causing the amino acid substitutions p.P206S (c.757C>T; exon 6), p.W303R (c.907C>T; exon 7), and p.R441H (c.1322G>A; also known as 1463G>A; exon 11) [27], [28], [29]. Here, TPH2 is linked to psychiatric disorder.