'Gene cause' of addiction

The chances of becoming addicted to cocaine could depend on genes, the Institute of Psychiatry has found.

It identified a gene variation where cocaine would more markedly inhibit a protein that controls removal of key mood chemical dopamine in the brain.

Two copies of the variant made people 50% more likely to be cocaine abusers.

DNA of 700 cocaine abusers and 850 other people were compared for the study, published online by Proceedings of the National Academy of Sciences.

Cocaine's action within the brain is relatively well understood.

Its key effect is that it strongly inhibits the action of a protein - DAT - which controls removal of excess dopamine from the junctions between nerve cells in the brain.

This leads to nerve cells effectively being overloaded with dopamine, which is thought to contribute to the "high" associated with taking cocaine.

The latest study identified a specific variation in the genetic code controlling production of the DAT protein.

People carrying two copies of this particular variant were 50% more likely to be cocaine dependent.

Treatment hope

Researcher Dr Gerome Breen said: "This study is the first large scale search for a genetic variant influencing the risk of developing cocaine addiction or dependence.

"The target we investigated, DAT, is the single most important in the development of cocaine dependence.

"It made sense that variation within the gene encoding DAT would influence cocaine dependence."

Analysis showed that cocaine was likely to inhibit the DAT response more markedly in people who carried the key genetic variant.

Dr Camila Guindalini, who also worked on the study, said: "This research helps our understanding of the development of cocaine addiction.

"It could influence the design and use of drugs to treat cocaine abuse in the future.

"Although repeated exposure to cocaine will lead to compulsive use in everyone, it seems some people will become addicted to the drug more quickly than others because of a genetic difference."

Harry Shapiro, of the charity DrugScope, said: "While genetics may have a role in helping us 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."