TUESDAY, Oct. 30 (HealthDay News) -- Smoking and attention-deficit/hyperactivity disorder (ADHD) share a common genetic risk factor, and childhood ADHD may increase the likelihood of smoking later in life, a new study suggests.
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People with ADHD are more likely to start smoking early and to smoke twice as much as those without ADHD, the researchers noted.
For the new study, the investigators took blood samples from more than 450 children with ADHD, aged 6 to 12, and their siblings and parents. The samples were tested for five genetic variations strongly associated with different aspects of smoking, such as the number of cigarettes smoked every day, and taking up and quitting smoking. The researchers also asked the mothers about their smoking habits during pregnancy.
A genetic variant associated with the number of cigarettes smoked by mothers during pregnancy was more likely than other variants to be associated with ADHD. It was also more likely to be passed on from parents to children and to be associated with more severe ADHD.
This variant was as likely to be found in children whose mothers smoked as it was in those whose mother's did not smoke during pregnancy, which suggests that exposure to tobacco smoke in the womb is not a factor.
The findings suggest that this genetic variant may increase the risk of both ADHD and smoking by prompting behaviors and impaired higher brain function that are typical of childhood ADHD, and which could lead to smoking later in life, concluded Dr. Ridha Joober, of the Douglas Mental Health University Institute in Montreal, and colleagues.
The study was published online Oct. 29 in the journal Archives of Disease in Childhood.
Although these are intriguing findings, further research is needed to determine whether there are actually shared genetic risks for smoking and ADHD, Miriam Cooper and Anita Thapar, of Cardiff University School of Medicine in Wales, wrote in an accompanying editorial.
Such research could lead to a better understanding about developmental and psychiatric disorders in children, the editorialists added in a journal news release.
Although the study found an association between the genetic variant and ADHD and smoking behaviors, it did not prove a cause-and-effect relationship.
-- Robert Preidt
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