Molecular genetic research has mainly focused on the D4 dopamine receptor (DRD4) and the dopamine transporter (DAT) genes in attention-deficit hyperactivity disorder (ADHD). A recent meta-analysis showed that the DRD4 gene has a significant role in the vulnerability to ADHD.
With an equal number of positive and negative association studies between the 10-repeat of the DAT gene and ADHD, a meta-analysis is required for this other candidate gene.
We re-analysed the 13 published family-based association studies between ADHD and the DAT gene. Following recent recommendations, different biases were specifically assessed, such as the sample-size effect and the time effect.
The meta-analysis showed no significant association between ADHD and the DAT gene (P=0.21), but an important between-samples heterogeneity (P=0.0009). Odds ratios above 1 are mostly observed in studies with a small number of informative transmissions, and decrease with larger sample size.
Contrary to what was found for the DRD4 gene, the 10-repeat allele of the DAT gene has at most a minor role in the genetic susceptibility of ADHD. The different biases detected herein probably explain the initial impression of a significant impact of the DAT gene on hyperactivity.