People who smoke, take street drugs or become heavy drinkers may be genetically predisposed to their habits, suggest the results of a large new study.
By combining 46 previous studies, scientists have definitively linked two genes to personality traits thought to make people more likely to take up risky lifestyles.
The analysis of the data from over 20,000 people linked a particular version of a gene for the transport of the neurotransmitter serotonin - 5HTT-LPR - to having a more anxious, neurotic personality.
And a version of the gene for a receptor of the neurotransmitter dopamine - the D4 receptor - was associated with having a more outgoing personality. It is well-established that both these personality traits are more likely to lead to substance misuse.
"Our study suggest that there's a genetic basis to certain kinds of personality trait, which may be important in influencing whether people take up habits like smoking or whether they can subsequently give them up," says Marcus Munafő, team leader of Cancer Research UK's GP research group in Oxford. In the future, pharmaceutical or behavioural treatments could be tailored to the type of person you are, he told New Scientist.
Among the health risks associated with substance misuse is an increased chance of cancer, notes Robert Souhami, director of clinical research at Cancer Research UK. "These people may be resistant to conventional health messages and may need subtler health warnings, or perhaps specific anti-addiction treatment for their particular personality type," he says.
Novelty seeking
The researchers analysed 46 studies examining the association between genes and behaviour. Munafő a psychologist, says that the individual studies have come to conflicting conclusions.
Only two genes were "robustly related" to behaviour, found the analysis. A short version of the serotonin transporter gene was strongly linked to neuroticism. Serotonin is known to control emotions like anxiety and depression. The short version of the gene was associated with lower levels of serotonin activity.
"If you have very high natural levels of anxiety you are more likely to smoke," says Munafő. "If you belong to the group with the short version of the gene, on average your neuroticism score will be 10 per cent higher."
But he adds: "It's high, but still only part of the story." Environment, such as childhood experience or diet, will also have a large influence on how genes are expressed.
Variations in the gene for the dopamine D4 receptor may affect how extravert a person is by altering the brain's response to the neurotransmitter, although this link was less strong. Dopamine is thought to be associated with novelty seeking behaviour and pleasure - which could make a person more likely to try new substances.
The group is currently analysing new data on how genes and personality influence nicotine dependence in a smoker. A relationship between the three "looks promising", says Munafő.
Journal reference: Molecular Psychiatry (vol 8, p 471)
