Variability of the tryptophan hydroxylase gene: study in victims of violent suicide

Tryptophan hydroxylase (TPH), the enzyme controlling serotonin synthesis, is considered to be a potential contributor to the biological substrate of suicide. The association of the promoter (-7065CT) and intron 7 (218AC) polymorphisms, and the related haplotype, of the Tph1 gene with suicidal behavior was investigated in a sample of 160 victims of violent suicide and 284 healthy controls. All individuals were males of Croatian (Slavic) origin. Allele frequencies of both polymorphisms in Croatian controls were similar to control values reported for other European populations. Alleles at the two loci demonstrated highly significant linkage disequilibrium. No differences between controls and victims for the Tph1 genetic variation, either at single loci, or at a haplotypic level, were demonstrated, albeit there was a tendency, not reaching statistical significance, towards an increase of the intron 7CC genotype in the suicide group. Negative association results on the individual Tph1 loci, in accordance with the majority of previous reports, confirmed the lack of their major effect also in the Slavic ethnicity. Haplotypic results, on the other hand, opposing the previous positive finding, point to the possible influence of ethnicity (or gender) on the association between the Tph1 gene polymorphism and suicide.