No evidence of association between the TPH gene and affective disorders

Serotonin neurotransmission is considered to contribute substantially to the pathophysiology of affective disorders. The gene for tryptophan hydroxylase (TPH), the rate-limiting enzyme of serotonin synthesis can, thus, be regarded as one of the candidate genes possibly implicated in the etiology of these disorders. The TPH gene, on chromosome 11p14-15.3, has been found to be associated with bipolar illness in one study, but other studies have produced negative results. The aim of the present study was to assess the possibility for a genetic association between the TPH gene and patients with affective disorder (bipolar and unipolar). Our sample consisted of 62 bipolar patients, 55 unipolar patients, and 50 controls (blood donors). All subjects were unrelated Greeks and were personally interviewed. Diagnoses were made according DSM-IV and ICD-10 criteria. The analysis was based on identification of a restriction enzyme digestion site. Allelic frequencies of the two alleles did not differ among the three groups of subjects, even after subgroups of patients according to their age of onset were separately analyzed. The results of the study do not provide any evidence in favor of genetic association between this polymorphism of the TPH gene and bipolar or unipolar affective illness.