Within the DRD4 gene, the 48 bp VNTR in exon III has received the most interest in psychiatric genetics [10,11]. Recent studies suggested that the 7-repeat allele of the DRD4 gene may result in reduced DRD4 expression, influencing RNA stability [27]. Therefore, other polymorphisms located in the promoter region of the DRD4 gene with predictable or proven effects on gene expression might also be worthwhile to study. The -616 C/G and -521 C/T SNPs, and a 120 bp duplication in the 5' untranslated region of the DRD4 gene have been extensively studied in dopamine-related child psychiatric disorders, such as ADHD [10]. Therefore, we have analyzed these four DRD4 gene variants in the two samples.
