Dopamine transporter gene polymorphism moderates the effects of severe deprivation on ADHD symptoms: Developmental continuities in gene–environment interplay

Early institutional deprivation is a risk factor for Attention‐Deficit/Hyperactivity Disorder (ADHD) symptoms. However not all individuals are affected. We tested the hypothesis that this heterogeneity is influenced by gene x environment (GxE) interaction and that genetic polymorphisms involved in dopamine neurotransmission moderate the effects of severe early institutional deprivation on symptoms of ADHD (sADHD). Using a prospective‐longitudinal design sADHD were measured at ages 6, 11, and 15 years in a sample of individuals who experienced severe institutional deprivation (up to 42 months of age) in Romanian orphanages and a non‐institutionalized comparison group. Individuals were genotyped for polymorphisms in the dopamine D4 receptor ( DRD4 48‐bp VNTR in exon 3) and dopamine transporter gene ( DAT1 haplotypes combining a 40‐bp VNTR in 3'UTR and a 30‐bp VNTR in intron 8). The risk for sADHD associated with early institutional deprivation was moderated by the DAT1 but not the DRD4 genotypes; an effect that was first apparent in early‐, and persisted to mid‐adolescence. The results (i) provide evidence for developmental continuities in G x E interaction, (ii) explain some of the heterogeneity in ADHD outcomes following institutional deprivation and, (iii) add to our understanding of environmental determinants of sADHD. © 2009 Wiley‐Liss, Inc.