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

Abstract

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.

Fig. 1

Papers have been grouped into one of the following racial categories: Asian, European-Caucasian, Middle Eastern and South American. Darkened diamonds correspond to group values while the white squares and line that cross through show the OR for each paper and the corresponding confidence interval.

Fig. 2

The countries that were included in this meta-analysis have been darkened on the map. The odds ratio and P-values are displayed for each race category. Odds ratio for the Asian category was not significant.

Fig. 3

Publication Bias measures the tendency that significant results are published while those that are not significant are kept from publication. This graph measures the publication bias of the European–Caucasian group. A scatterplot shaped similar to the Isosceles triangle indicates little publication bias, while a scatterplot that varies from the triangle shows that publication bias is an issue. This figure shows that publication bias is an issue in reporting the relationship between ADHD and the 7R allele.