The study states that prenatal exposure to smoking in the mother's womb puts genetically susceptible children at an increased risk the disorder.
During the course of study, the researchers studied male and female twin pairs, aged 7-19 years, so as to assess the relationship between genetic variations, prenatal substance exposures, and ADHD sub-types.
"When genetic factors are combined with prenatal cigarette smoke exposure, the ADHD risk rises very significantly. When the child has either or both of two specific forms of dopamine pathway genes (DAT and DRD4), and was exposed to cigarette smoking in utero, the risk for having combined type ADHD (many inattention and hyperactive/impulsive symptoms) increased 3 to 9 fold," explained Dr. Rosalind, one of the study's authors.
"These data highlight a new risk of maternal smoking, increasing the risk for ADHD in their children. ADHD, in turn, increases the risk for substance abuse. Thus, it appears that in utero exposure to nicotine may help to perpetuate a cycle across generations that links addiction and behavioural problems," added Dr. John H. Krystal, Editor of Biological Psychiatry.