Harvard researchers may have found a link to nicotine exposure and ADHD.
A higher rate of exposure to paternal smoking at conception among youth with attention-deficit/hyperactivity disorder (ADHD) than in those without suggested an association that had been suspected from preclinical findings. But the link became less clear when researchers considered the genetic influence of the fathers who also had ADHD.
Recent preclinical evidence of nicotine exposure mediating risk for hyperactivity in rodent offspring was the basis to investigate the possible association with ADHD in humans, according to Joseph Biederman, MD, chief of Clinical and Research Programs in Pediatric Psychopharmacology and Adult ADHD, Harvard Medical School, Boston, Massachusetts, and colleagues.
"These findings suggested that that nicotine exposure may adversely impact germ lines, supporting a novel hypothesis for the propagation of environmentally induced ADHD phenotypes in the population that includes paternal smoking during conception," explained Biederman and colleagues.
The investigators accessed data from a longitudinal, case-control family study of girls with and without ADHD, to examine the possible association with paternal smoking. They identified 121 girls with a diagnosis of ADHD and 105 without, having fathers who had reported smoking at least one pack of cigarettes a day on the Structured Clinical Interview for DSM--R (SCID). The two groups of girls were of similar age and socioeconomic status.
Thirty-five percent of the girls diagnosed with ADHD had been exposed to paternal smoking at conception, compared to 23% of those without ADHD. The investigators calculated an odds ratio (OR) of 1.5 for paternal smoking having increased risk for development of ADHD
The putative association lost statistical significance, however, after controlling for paternal ADHD. The investigators attribute this, "most likely due to limited statistical power."
Biederman and colleagues still consider the association feasible, and anticipate that it will be investigated further in studies with larger populations of children of both sexes, with sufficient statistical power to control for other risk factors such as maternal smoking during pregnancy and comorbidity.
Finding that the fathers in the cohort who smoked were also more likely to have ADHD is consistent with previous documentation of that association. Biederman and colleagues point out that genes involved in dopamine function and with nicotinic receptor activity have been associated with both ADHD and smoking addiction.
"Clearly, more work is needed to disentangle the environmental effects of paternal smoking at conception from genetic contributions," Biederman and colleagues expressed.
The study on paternal smoking as a risk factor for ADHD was published on-line February 2 in the Journal of Attention Disorders, "Is Paternal Smoking at Conception a Risk for ADHD? A Controlled Study in Youth With and Without ADHD."