DRD4 and attention deficit-hyperactivity disorder: These findings suggest that the 4-repeat allele of DRD4 gene plays a protective role against inattention and impulsivity of ADHD symptoms.21,22 This is consistent with previous work23 in which higher scores of commission errors in CPT had been measured in ADHD children with 7-repeat allele of DRD4, while lower omission errors and commission errors had been measured in patients with homozygosity of the 4-repeat allele of DRD4 genes.