Determination of association between the polymorphism in exon 3 of dopamine receptor gene type 4 with attention deficit-hyperactivity disorder

Introduction: Evidences suggest that attention deficit-hyperactivity disorder (ADHD) is a hereditary disorder and at least 20 potential genes associated with ADHD have been identified. Dopamine receptor gene type 4 (DRD4) has been more considered due to a stronger relationship with ADHD. However, no study has yet been conducted on the Iranian population to assess the association. Objective: In this study, the association between polymorphism of DRD4 gene with ADHD has been studied among capital of Iran population. Materials and methods: This study is a case-control study conducted on children aged 6-12 years with ADHD referred to child and adolescent psychiatric clinic Imam Hussein (AS) and normal subjects in 2011. Diagnosis was done based on the DSM-IV-TR criteria and interviewing by two child and adolescent psychiatrists. If parental were consent, then saliva samples of subjects were prepared and DRD4 gene and related allele were evaluated using PCR method. The K-SADS questionnaire was also used to assess comorbid disorders. Results: In this study, 114 patients in ADHD group and 109 patients in the control group were studied. The most frequency was obtained for allele 4 allele that has been observed in about 90% of both case and control groups. However, frequency of allele 6 in the case group was 8.8% where the frequency was 5% in the control group (p = 0.02). The presence of repeat of allele 6 increased chance of suffering from ADHD to 1.809 (95% equal to 3.871-0.845). Conclusion: For the first time this study showed that in Iranian population repeat of DRD4 gene allele 6 unlike the other geographic areas is relatively common and it will increase the chances of suffering from ADHD. However, additional studies are required.