Effect of Tryptophan Hydroxylase Gene Polymorphism on Aggression in Major Depressive Disorder and Undifferentiated Somatoform Disorder

Abstract

Aggression and anger have been linked with depression, and anger suppression has been linked with somatic symptoms of somatoform disorders. However, the relationship between aggression or anger and genes in patients with depression and somatoform disorders has not been clearly elucidated. The objective of this study was to examine the effect of serotonin-related gene polymorphism on aggression in depressive disorders and somatoform disorders. A serotonin-related polymorphic marker was assessed by using single nucleotide polymorphism (SNP) genotyping. 106 outpatients with major depressive disorder (MDD), 102 outpatients with undifferentiated somatoform disorder, and 133 healthy subjects were enrolled between October 2005 and May 2008. Diagnoses were made according to the Korean version of the Structured Clinical Interview Schedule for DSM-IV. The allele and genotype frequencies of tryptophan hydroxylase-1 (TPH1) A218C were compared between groups. The Hamilton Depression Rating Scale and the Aggression Questionnaire were used for psychological assessment. Each of the 2 disorder groups scored significantly higher on all the Aggression Questionnaire subscales and on the total Aggression Questionnaire score than the healthy subjects (P < .001). Patients with MDD had significantly higher frequencies of TPH1 C allele (P = .0002) and CC homozygote (P = .0003) than healthy subjects, regardless of sex and age. However, no significant differences were found in TPH1 C allele and CC homozygote frequencies between the undifferentiated somatoform disorder patients and the healthy subjects. TPH1 CC homozygote in the MDD group scored significantly higher in terms of verbal aggression (P = .03) and total Aggression Questionnaire score (P = .04) than A-carrier genotypes, regardless of sex and age. However, no significant differences were found in the scores of all the Aggression Questionnaire subscales and the total Aggression Questionnaire score between TPH1 CC homozygote and A-carrier genotypes in the undifferentiated somatoform disorder group and the control group, respectively. Aggression in MDD patients is more susceptible to an excess of TPH1 CC homozygote than in undifferentiated somatoform disorder patients, though the 2 disorders are high risk groups for aggression. In addition, TPH1 gene is most likely to have a shared effect on aggression and MDD.