Association analysis of four human dopamine pathway genes with adult attention-deficit hyperactivity disorder in a population from Turkey

In this tudy, it was aimed to investigate the association/s between dopamine transporter gene (DAT1), dopamine receptor D1 (DRD1), dopamine receptor D2 (DRD2), dopamine receptor D3 (DRD3), dopamine receptor D4 (DRD4) gene variants and adult Attention Deficit and Hyperactivity Disorder (ADHD). A prospective analytical case control study. A total of 128 ADHD cases and 100 non-ADHD controls from Western population of Turkey were included in this study. DNA was isolated from peripheral blood. Genotype and allele frequency P-values were calculated by Chi square (c2) and Fisher Exact tests. Other statistical analyses were carried out using SPSS program version 20.0. The genotypes for the DAT1, DRD2, DRD3 and DRD4 variants were identified by polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP). 4R allele and 4R/4R genotype of Exon 3 VNTR polymorphism in the DRD4 gene were observed to be the most frequent one in both case and control groups. 4R allele was found to be statistically significant in ADHD group than the ones in control group (p=0.01). No statistical differences in the genotype and allele frequencies were observed between ADHD cases versus non-ADHD controls for DAT1, DRD2 and DRD3 polymorphisms. A statistically significant association was found only between DRD4 Exon 3 VNTR polymorphism and adult ADHD. However, to confirm that these gene variants contributes to ADHD and ADHD-subtypes, further studies with both higher population sizes and many candidate genes are needed to be investigated simultaneously.