Dopamine transporter gene (DAT1) polymorphism associated with emotional and behavioral problems in children with attention-deficit / hyperactivity disorder (ADHD)

Background: It was suggested that the dopamine transporter gene (DAT1) was associated with ADHD (Attention-Deficit/Hyperactivity Disorder). The major polymorphism of the DAT1 involves a variable number of tandem repeats (VNTR) situated in the 3′ untranslated region of the gene. The 10 repeat allele (480 bp) was reported to be high risk allele for ADHD. It was suggested that the response to drug and clinical characteristics differed according to the type of DAT1 polymorphism in ADHD. The 10 repeat allele was related to the symptoms of internalizing disorders in both clinically referred children and controls. The 9 repeat allele (440bp) was related to the externalizing behavior problems in a community sample of children. On the bases of these findings, it is expected that children with ADHD show different emotional and behavioral problems according to the DAT1 polymorphism. Method: Thirty-seven unrelated ADHD patients were recruited. Genomic DNA was extracted from the blood, and analyzed by a polymerase chain reaction(PCR) to determine the genotype. Parents filled in the Korean-Child Behavior Checklist (K-CBCL) to evaluate the emotional and behavioral problems of the children. The K-CBCL subscale scores were compared to the 10/10 genotype and the 10/9 genotype using a Mann Whitney U test. The correlation between the attention problems score and other subscale scores were computed using a Spearman's correlation test in each group. Result: The thought problems score was higher in the 10/9 genotype than in the 10/10 genotype(Z=0.024, p<0.05). In the 10/10 genotype, the attention problems score negatively correlated with the social competence and positively correlated with the withdrawn, anxious/depressed, social problems, thought problems, delinquent behavior and aggressive behavior but not in the 10/9 genotype. Conclusion: Patients with the 10/10 genotype and patients with the 10/9 genotype appear to have different emotional and behavioral problems. Patients with the 10/9 genotype have a risk of thought problems, which may require intervention. In the 10/10 genotype, the more severe the attention problem is, the more clinical attention is needed to treat the comorbid emotional and behavioral problems. However, the small sample size of this study is a limitation to generalizing these results. A further study with a larger sample is currently underway.