A variation of a particular gene appears to be shared between ADHD and smoking, making ADHD sufferers more likely to be smokers, according to research published in the Archives of Disease in Childhood.
The researchers looked at five variations in DNA sequences in different genes that are strongly associated with different aspects of smoking behavior, such as the number of cigarettes smoked every day, and taking up and quitting smoking. They wanted to see if these might also be linked to hyperactivity aged between 6 and 12 with confirmed ADHD.
They found that only one of the five variations (the one associated with the number of cigarettes smoked) was associated with ADHD.
The researchers said the high risk variation was significantly more likely to be passed on from the parents and to be associated with the more severe form of ADHD.
Interestingly, the variation was as likely to be found in children whose mothers had smoked during pregnancy as those who hadn't, suggesting that environmental tobacco smoke does not modify the risk.
While the variation may increase the risk of both ADHD and smoking, the researchers caution that the findings should only be interpreted as preliminary evidence. The theoretical plausibility for shared molecular genetic risks for smoking and ADHD needs to be tested in further larger studies, they suggest.
"Acknowledging that the same genetic risk variants can have different observable effects in people could help inform discovery of risk variants for childhood developmental/psychiatric disorders," the study notes. "Such efforts could help uncover novel biological risk pathways and contribute to explaining why different behaviors and disorders commonly co-occur."
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Source: British Medical Journal