SLC6A3 and attention deficit-hyperactivity disorder: Our a priori hypotheses were that we would replicate G × E findings originally reported in studies conducted in HIC, with (a) adolescents homozygous for the 10-repeat allele in the DAT1 gene showing higher levels of ADHD symptoms when maternal smoking was present during pregnancy, and (b) male adolescents with low activity MAOA genotype presenting higher levels of CD when childhood maltreatment was reported.