[Effects of the D4 dopamine receptor gene variation on behavior problems at 6 years of age]

Association of the 7-repeat allele of the D4 dopamine receptor (DRD4) exon 3 polymorphism with attention deficit/hyperactivity disorder is well-established, and a link with mother-reported aggressiveness was also found in healthy pre-schoolers assessed by the quantitative scale of the Child Behavior Checklist. In the present study, we hypothesized that children carrying the 7-repeat allele would show more attention problems and externalizing (aggressive and delinquent) behavior at 6 years of age. Further, we hypothesized a potential mediating role of early temperament in the relationship of DRD4 gene with behavior problems. Mothers filled in the Achenbach Child Behavior Checklist for 88 six-year-old firstborn children (51 boys, 35 girls) followed from birth. Mother-reported temperament for the same children was assessed by the Rothbart Infant Behavior Questionnaire at 12 months. Genotypes of the DRD4 repeat polymorphism were determined using buccal cells. Significant main effects of gender and DRD4 genotype were observed on 6-year behavioral problems. Boys showed more attention problems and externalizing behavior, and children lacking the 7-repeat variant showed more externalizing and internalizing behavior. These effects remained significant after controlling for 1-year temperament. Our results did not confirm the negative effect of the 7-repeat allele on attention problems and externalizing behavior measured on quantitative scales. On the contrary, we found elevated problem scores in the absence of the 7-repeat allele. Further research including environmental risk factors is needed to clarify the role of the DRD4 gene in the development of externalizing behavior.