Don't blame genes for alcoholism, says top brain scientist

Alcohol dependence is not caused by a special gene found in a minority of problem drinkers.

This was one of the messages of Baroness Susan Greenfield, the UK's best known neuroscientist addressing an audience at the Royal Institution of Great Britain in central London. There was some irony in Baroness Greenfield's dismissal of the idea of a gene for alcoholism, as she was lecturing to an invited audience on behalf of the alcohol industry's Portman Group. Traditionally, the industry has been rather attracted to the idea that alcohol dependence 'comes in people' – in genes - rather than in bottles.

Baroness Greenfield, while accepting that there may be a genetic predisposition to alcoholism, explained that such a simplistic view must be mistaken.

"Alcoholism can't be locked into the structure of DNA any more than good housekeeping or being witty can." she said. "Genes are as important to brain function as sparking plugs are to car engines(but) a sparking plug does not have 'movement' trapped inside it. Its potential is only realised when it is placed in an engine, the engine into a car and the car has a driver."

Similarly, Baroness Greenfield continued, with genes. They may be necessary for some behaviour to occur but they are not sufficient. This, she said, could hardly be otherwise given that the human body contains only 30,000 genes whereas there are 1,000,000,000,000,000 brain connections. Genes merely make proteins. The expression of a protein, even in the correct micro-environment has in addition to be nested in the hierarchy of integrated brain circuits and overlapping brain regions and placed within a whole body in order for the effects, the final behaviour, to appear. Only if a gene is defective does an impairment such as predisposition to alcoholism become apparent.

Baroness Greenfield also took the opportunity to attack currently fashionable arguments for the legalisation of cannabis. She rejected in particular the idea that cannabis and alcohol are equivalent in their adverse effects. In the first place, she explained, cannabis and alcohol act on the brain in a fundamentally different way.

Although alcohol enters the brain easily, it requires at least 7,000mg (slightly less than one standard unit) to have a perceived effect on consciousness. In contrast, cannabis has a harder time gaining access to brain cells, yet can have an effect as low as 0.3mgs. Moreover, while one unit of alcohol can be cleared from the body in an hour, THC, the active ingredient of cannabis, can remain in the body for 120 hours.

The more concentrated effects of cannabis on the brain help to explain why even low, "social' levels of consumption can have a range of adverse effects that low consumption of alcohol does not. Cannabis, unlike alcohol enhances the risk of psychotic episodes and schizophrenic side-effects, even at low levels of consumption and in individuals who have never exhibited such symptoms before.

Also, with cannabis but not with alcohol, even when the drug is no longer used long-term effects on cognition and attention can persist. The risk of dependence is also greater with cannabis. Ten percent of cannabis users who want to stop have problems doing so, and there are withdrawal effects after only three days of very moderate use of cannabis.