We reported a positive association between the intron 7 A218C polymorphism of the TPH gene and bipolar affective disorder in a sample of 158 bipolar patients (103 with bipolar I and 49 with bipolar II) and 94 controls.1 However, 2 subsequent studies failed to confirm this finding. Kirov et al2 show no preferential A218C allele transmission in a sample of 118 parent-offspring trios and McQuillin et al3 failed to replicate the initial finding in a case-control association study.
Bellivier F, Leboyer M, Courtet P, Feingold J, Buresi C, Malafosse A. No Allelic Association Between Bipolar Affective Disorder and the Tryptophan Hydroxylase Gene—Reply. Arch Gen Psychiatry. 1999;56(1):101. doi: