A specific allele of this gene (known as the 'DRD4 long' variant) has been loosely linked to a susceptibility for developing ADHD and a variety of other psychological traits.
↑Faraone SV, Doyle AE, Mick E, Biederman J. (2002) Meta-analysis of the association between the 7-repeat allele of the dopamine D(4) receptor gene and attention deficit hyperactivity disorder. Am J Psychiatry. 158(7):1052-7. PMID 11431226free full text