ADHD and the DRD4 exon III 7-repeat polymorphism: an international meta-analysis.

We sought to elucidate the relationship of ADHD (Attention-Deficit Hyperactivity Disorder) to the DRD4 exon III VNTR 7R allele worldwide using analytic techniques and to relate these findings to the field of cultural neuroscience. To focus on a potential moderating role of race/ethnicity, we excluded over 30 papers that have explored the relationship between the DRD4 7R and ADHD but had unclear or lax racial-ethnic inclusion criteria. The papers in this meta-analysis were only included if a single race made up 95% or more of their sample. We searched for and translated papers not published in English, and found a significant difference in the relationship of ADHD and DRD4 7R in people of European-Caucasian (Odds ratio 1.635, Z = 3.936, P < 0.00001) and South American (Odds ratio 2.407, Z = 3.317, P = 0.001) descent vs people of Middle Eastern ancestry (Odds ratio 0.717, Z = -2.466; P = 0.014). We also examined the moderating effect of differing ADHD diagnoses, subject recruitment, control recruitment and male to female ratio. Finally, we consider the implications of these data for cultural neuroscience.