Further replication of these findings in additional large case-control and family-based association is needed before TPH can be designated a risk gene for bipolar disorder.
The homozygous recessive genotype of the TPHA218C polymorphism has a significant effect on risk for bipolar disorder but not major depressive disorder.
Although the tryptophan hydroxylase isoform-1 gene (Tph1) has been reported to have a genetic association with bipolar disorder and schizophrenia, the Tph1 isoform is expressed at much lower levels than Tph2 (150-fold less in the mouse brain).
Although the tryptophan hydroxylase isoform-1 gene (Tph1) has been reported to have a genetic association with bipolar disorder and schizophrenia, the Tph1 isoform is expressed at much lower levels than Tph2 (150-fold less in the mouse brain).