The DRD4 receptor Exon 3 VNTR and 5' SNP variants and mRNA expression in human post-mortem brain tissue

Genetic variation within the dopamine D4 receptor (DRD4) gene has been implicated in many neuropsychiatric disorders and behavioral traits. This variation includes the extensively studied exon 3 variably numbered tandem repeat (VNTR), and several 5' polymorphisms including a120-bp duplication and two single-nucleotide polymorphisms at -521 C/T (rs1800955) and -616 C/G (rs747302). Several reports have provided evidence for a functional role for some of these variants using in vitro techniques. This study investigated the functionality of these polymorphisms in 28 human post-mortem brain tissue samples by quantifying DRD4 mRNA expression in relation to genotype. No statistically significant relationship between genotype and mRNA expression levels was found for these four polymorphisms although a weak trend toward the 7-repeat of the exon 3 VNTR reducing DRD4 mRNA expression was found. Employing post-mortem brain tissue, rather than using in vitro techniques may provide a more relevant paradigm to study functional effects of reported risk alleles.