Functional Impact of An ADHD-Associated DIRAS2 Promoter Polymorphism

Abstract

The DIRAS2 gene is coding for a small Ras GTPase with so far unknown function. In a previous study, we described the association of DIRAS2 rs1412005, as well as a haplotype containing this polymorphism and located in the promoter region of this gene with attention-deficit/hyperactivity disorder (ADHD). In the present study, we searched for rare variants within or near the DIRAS2 gene that might be associated with ADHD using next-generation sequencing. As we were not able to detect any rare variants associated with the disease, we sought to establish a functional role of DIRAS2 rs1412005 on the molecular or systems level. First, we investigated whether it has an influence on gene expression by means of a luciferase-based promoter assay. We could demonstrate that the minor risk allele goes along with the increased expression of the reporter gene. Next, we aimed to identify differences in response inhibition between risk-allele and non-risk allele carriers in children suffering from ADHD and healthy control individuals by analyzing event-related potentials in the electroencephalogram during a Go/NoGo task. Risk-allele carriers showed a changed NoGo anteriorization. Therefore, our results suggest an impact of the investigated polymorphism on the prefrontal response control in children with ADHD. These results imply that the promoter polymorphism is indeed the associated as well as in itself a causal variant. Further research is thus warranted to clarify the mechanisms linking DIRAS2 to ADHD.

Figure 1

Schematic of the DIRAS2 gene taken from the UCSC Genome Browser (http://genome.ucsc.edu/) showing the positions of the amplicons used for NGS (black bars) and the variants investigated in the replication (red triangles). A full color version of this figure is available at the Neuropsychopharmacology journal online.

Figure 2

Boxplot showing the combined z-scores for the three luciferase activity measurements in SH-SY5Y cells of the DIRAS2 SNP rs1412005. The luciferase activity is significantly higher (p=4.207 × 10⁻⁵) in cells transfected with the constructs containing the minor allele of the DIRAS2 promoter polymorphism.

Figure 3

Position of the centroids in the Go/NoGo task in risk-allele carriers and non-risk allele carriers. In individuals lacking the risk allele of the DIRAS2 promoter polymorphism, no NoGo anteriorization could be found. Statistically significant difference is indicated by an asterisk (p = 0.001).