In the case of DRD4, subjects were classified depending on the presence/absence of VNTR variants previously linked to ADHD in the exon III of DRD4, with carriers of at least one copy of the 7R or 2R allele considered as the risk group and homozygous for 4R as the controls/non-risk group. The gene discussed is DRD4; the disease is attention deficit-hyperactivity disorder.