We read with interest the article on a positive association between a polymorphism in the tryptophan hydroxylase (TPH) gene and manic-depressive illness.1 The authors found a significantly increased rate of the "A" allele in patients compared with control subjects (52% vs 36%).1 The TPH gene encodes for the rate-limiting enzyme of serotonin synthesis, making it a strong candidate gene for manic-depressive disorder; therefore, we attempted to replicate these results.
Kirov G, Owen MJ, Jones I, McCandless F, Craddock N. Tryptophan Hydroxylase Gene and Manic-Depressive Illness. Arch Gen Psychiatry. 1999;56(1):98–99. doi:10.1001/archpsyc.56.1.98