Some studies reported that the DAT1-prenatal maternal smoking interactions were significant only in boys homozygous for the 10-repeat allele and only for hyperactive-impulsive symptoms (Altink et al., 2008; Becker et al., 2008), while another, smaller study found no interaction effect for DAT1 and prenatal maternal smoking on ADHD (Langley et al., 2008). The gene discussed is SLC6A3; the disease is attention deficit-hyperactivity disorder.