Excess Tryptophan Hydroxylase 17 779C Allele in Surviving Cotwins of Monozygotic Twin Suicide Victims

Objective: To evaluate the relationship of the tryptophan hydroxylase (TPH) genotype to suicidality by the study of surviving monozygotic (MZ) cotwins of twins who committed suicide. Method: Twenty-four surviving Swedish MZ twins whose MZ cotwins had committed suicide were compared to 158 demographically sampled Swedish general population controls for TPH alleles. We also examined serotonin transporter alleles. Results: The living MZ cotwins of suicide victims had a significantly higher TPH 17 779C allele frequency than controls. No significant difference was observed for serotonin transporter alleles. Conclusion: These results, in a small sample, suggest the possibility that the 17 779C allele of the TPH gene may be associated with an increased risk of suicide. Further studies in larger samples are needed.