Gene clue to cocaine addiction

UK researchers have linked variations in a key brain chemical gene to the ease with which a person will become addicted to cocaine. The team, based at the Institute of Psychiatry, Kings College London, says that although everyone who repeatedly takes cocaine will eventually become addicted, different versions of the DAT (dopamine active transporter) gene could mean that some become dependent on the drug more quickly than others. The findings, published online in the Proceedings of the National Academy of Sciences, could eventually lead to new treatments for cocaine addiction.

Cocaine and other drugs 'hijack' the brain's reward circuit, which involves the production of the chemical dopamine - normally triggered by food and sex, amongst other things. The DAT gene makes a protein that controls the removal of excess dopamine. Cocaine stops DAT from working properly, which leads to a dopamine overload in the brain, producing the 'high' obtained after taking the drug. The researchers investigated different versions of the DAT gene, to see if they had any effect on cocaine addiction.

The team studied DNA samples from 1565 people living in Brazil, 699 of whom had a history of cocaine dependency. The other 866 participants had no past history of drug abuse. The scientists found that one particular version of the DAT gene was linked to an increased risk of dependency - people with two copies of this variant were 50 per cent more likely to become addicted. It seems that in such individuals, cocaine is more effective at blocking the DAT protein's action. Since DAT is the single most important protein in cocaine addiction, 'it made sense that variation within the gene encoding DAT would influence cocaine dependence', said team leader Gerome Breen.

Harry Shapiro, of the UK charity DrugScope, said that while genetics may have a role in helping to understand the nature of addiction, 'it would be wrong if this kind of research encouraged governments not to tackle the economic and social root causes of chronic, endemic drug use by instead focusing on individual pathology'.