Expression of the dopamine transporter gene is regulated by the 3′ UTR VNTR: Evidence from brain and lymphocytes using quantitative RT‐PCR

Abstract

Genetic association studies provide considerable evidence that the 10-repeat allele of a variable number tandem repeat (VNTR) in the 3'-untranslated region (3'-UTR) of the dopamine transporter gene (DAT1) is associated with a range of psychiatric phenotypes, most notably, attention deficit hyperactivity disorder. The mechanism for this association is not yet understood, although several lines of evidence implicate variation in gene expression. In this study, we measured DAT1 messenger RNA levels in cerebellum, temporal lobe, and lymphocytes using quantitative real-time reverse-transcription polymerase chain reaction. Relative to a set of four control housekeeping genes (beta-actin, GAPD, ribosomal 18S, and beta2-microglobulin) we observed that increased levels of DAT1 expression were associated with the number of 10-repeat alleles. These data provide direct evidence that the VNTR, or another polymorphism in linkage disequilibrium with the VNTR, is involved in regulating expression of this gene.

Dopamine Transporter 3′-UTR VNTR Genotype and ADHD: a Pharmaco-Behavioural Genetic Study with Methylphenidate

“…In vivo studies using imaging approaches (Heinz et al, 2000;Jacobsen et al, 2000;van Dyck et al, 2005) led to conflicting results (see Martinez et al, 2001 for a detailed discussion), which may be due to several methodological considerations, including the fact that the 9/9 genotype was very underrepresented in all the studies and was either excluded or grouped with the 9/10 genotype. Mill et al (2002) reported decreased levels of DAT1 mRNA levels in post-mortem brain tissue of patients having the 9/9 genotype, compared to the 9/10 and 10/10 genotypes. This result was consistent with an in vivo expression study, using the luciferase reporter system in COS-7 cells, which showed that the 7-and 9-repeat alleles had lower levels of transcription than the 10-repeat allele (Fuke et al, 2001), although opposite results using other experimental systems were also reported (Miller and Madras, 2002).…”

Dopamine Transporter Genotype and Methylphenidate Dose Response in Children with ADHD

“…Indeed, the contrast of 9/10 with 10/ 10 genotypes is not where our data suggest the most interesting question is, but rather between 9/9 vs 9/10 and 10/10 genotypes. Of most relevance, Mill et al (2002) demonstrated decreased DAT1 expression associated with the 9/9 genotype relative to genotypes containing the 10-repeat allele in human brain tissue and lymphocytes. As suggested by Kirley et al (2003), these studies provide intriguing clues regarding the relationship between variability in the length or sequence of the 3 0 -UTR of the DAT1 gene and levels of DAT1 in the brain, which will hopefully lead to more basic studies than can attempt to identify specific mechanisms.…”

Association between Dopamine Transporter (DAT1) Genotype, Left-Sided Inattention, and an Enhanced Response to Methylphenidate in Attention-Deficit Hyperactivity Disorder

“…For example, Fuke et al (2001) showed that the 10-repeat allele, relative to the 7-or 9-repeat alleles, increased gene expression using a reporter system. Mill et al (2002) also reported that mRNA levels in human brain and lymphocyte tissue varied with DAT1 VNTR, being higher in individuals with the 10-vs 9-repeat allele. Based on this evidence of differential gene expression as a function of VNTR alleles and the low frequency of individuals homozygous for the non-10-repeat alleles (less than 5% in the current sample), we compared the Landmark Asymmetry Indices of those ADHD probands without the 10-repeat DAT1 allele and those in possession of one copy of this allele (designated as Low-Risk DAT1) (n ¼ 21) to those in possession of two copies of this allele (designated as High-Risk DAT1) (n ¼ 22).…”