A new study shows that children who have been diagnosed with attention deficit hyperactivity disorder (ADHD) are more likely to start smoking early and to smoke twice as much as those without the condition.

Researchers discovered a variation of a particular gene that links the behaviors typical of ADHD with those associated with smoking.

The researchers focused on five variations in DNA sequences (single nucleotide polymorphisms or SNPs) in different genes that are associated with different aspects of smoking behavior to see if these were linked to hyperactivity in 454 children (ages 6 to 12) who had been diagnosed with ADHD. Smoking behaviors measured included things such as the number of cigarettes smoked every day, and taking up or quitting smoking.

They quizzed the children’s mothers about their smoking during pregnancy. Of those 394 mothers for whom they had information, 171 had smoked during pregnancy and 223 had not.

The researchers then assessed the extent of the children’s behavioral and emotional problems at home and at school, as well as their intellectual capacity, using a battery of tests.

They also took blood samples from the children, their parents, and siblings to see if any high risk variants — known as alleles — of the five genetic markers had been passed on, and if these were associated with the behaviors and impaired cognitive performance characteristic of ADHD.

They discovered that only one of the five SNPs (rs 1329650), which was associated with the number of cigarettes smoked, was more likely to be associated with ADHD.

The researchers report that the high risk C allele of rs 1329650 was significantly more likely to be passed on from the parents and to be associated with the more severe form of ADHD.

It was much more common among children who had higher scores on the validated behavioral tests, the researchers note, adding children who performed less well on tasks requiring more brain power and concentration were also more likely to inherit this risk allele.

The researchers hypothesize that the C allele of rs1329650 may increase the risk of both ADHD and smoking through prompting behaviors and impaired higher brain functions that are typical of childhood ADHD, and could act as a gateway to smoking later in life.

Source: British Medical Journal

Cigarette and lighter photo by shutterstock.

ADHD May Have Genetic Ties to Smoking