Objective : The definite causes of obsessive-compulsive disorder (OCD) are still unknown. Evidences from familial, twin and segregation studies support the role of a genetic component in the etiology of OCD. There are growing evidences that OCD has specific neurochemical and neuroanatomical basis. It has been shown that serotonergic neurons play the predominant pathophysiological role in OCD. Recently, it has also been proposed that neurotransmitters other than serotonin play a role in the pathophysiology of OCD, and a series of studies have provided evidence that dopamine is involved in some OCD patients. Therefore, the aims of this study were to investigate the association between dopamine receptor D4 (DRD4) and OCD.
Methods : One hundred and fifteen OCD patients and 160 normal controls participated in this study. Genomic DNA was extracted from their blood. The genotypes and allele frequencies of the DRD4 polymorphism between OCD group and control group were compared. OCD patients were classified into early onset group (age of onset <17) and late onset group (age of onset ≥17) according to their onset age and the genotype and allele frequency were compared between two groups. Using principal component analysis, we had already derived 4 factors from 13 main contents of YBOCS checklist in the previous study and in this study, we investigated the association between these three factors and DRD4 genotypes.
Results : In this case-control study, we could find that the L-genotype frequencies of DRD4 were significantly higher in OCD than in normal control groups (χ² test, p=0.04). There were no difference in genotype frequencies between early onset OCD group and late onset OCD group. In OCD group, patients with L-genotype had higher scores for the religious/somatic factor than the other groups (t test, p=0.009).
Conclusions : The Lgenotype of DRD4 may have negative effects on the development of OCD and religious/somatic factor of the obsessive-compulsive symptoms.
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