TPH1 was first discovered to support serotonin synthesis in 1988 by converting tryptophan into 5-hydroxytryptophan.[6] It was thought that there only was a single TPH gene until 2003. A second form was found in the mouse (Tph2), rat and human brain (TPH2) and the original TPH was then renamed to TPH1.[7]
^Finocchiaro LM, Arzt ES, Fernández-Castelo S, Criscuolo M, Finkielman S, Nahmod VE (December 1988). "Serotonin and melatonin synthesis in peripheral blood mononuclear cells: stimulation by interferon-gamma as part of an immunomodulatory pathway". J. Interferon Res. 8 (6): 705–16. doi:10.1089/jir.1988.8.705. PMID3148005.
^Walther DJ, Peter JU, Bashammakh S, Hörtnagl H, Voits M, Fink H, Bader M (January 2003). "Synthesis of serotonin by a second tryptophan hydroxylase isoform". Science. 299 (5603): 76. doi:10.1126/science.1078197. PMID12511643. S2CID7095712.