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Gene links cannabis use and mental illness

15 April 2005
By BioNews
Appeared in BioNews 304

A person's risk of developing a psychotic illness such as schizophrenia after smoking cannabis as a teenager is affected by their genetic make-up, say UK researchers. A new study to be published in the journal Biological Psychiatry shows that a variant of the COMT (catechol-O-methyl transferase) gene is linked to a five-fold increased risk of psychotic illness in people who have smoked the drug. The scientists, based at the Institute of Psychiatry at King's College London, say that neither cannabis nor the genetic variation alone is enough to trigger psychosis.

The team looked at a group of 803 people born between April 1972 and March 1973 in Dunedin, New Zealand, who have been tracked since birth as part of a long-term health study. According to a report in the Times newspaper, the participants were asked about their cannabis use at the ages of 13, 15 and 18. They were also tested to see what form of the COMT gene they had inherited, since this gene has previously been linked to schizophrenia. This illness is one of several psychotic disorders thought to involve an imbalance in levels of dopamine, a key brain chemical.

The COMT gene comes in two different varieties, known as 'val' and 'met'. In people with two met versions of the gene, the rate of psychotic illness was three per cent, regardless of whether they had smoked cannabis as a teenager or not. But in people with two val versions, the rate was 15 per cent in cannabis smokers, compared to three per cent in non-smokers. The findings suggest that the val gene variant and cannabis both affect the brain's dopamine system, delivering a 'double dose' that can be damaging. The group has previously published research showing that variations in another brain chemical gene affect how well a person copes with stressful life events, and their subsequent risk of depression.

Marjorie Wallace, chief executive of the mental health charity Sane, said that it was becoming clear that cannabis placed millions of users at risk of lasting mental illness. 'If we were able genetically to identify the vulnerable individuals in advance, we would be able to save thousands of minds, if not lives', she said. However, study leader Avshalom Caspi disagreed, saying that 'such a test would be wrong more often than it is right'. He said that since smoking cannabis has 'many other adverse effects', even people who are not genetically vulnerable should not be encouraged to use the drug.

One in four at risk of cannabis psychosis
The Times |  12 April 2005
1 August 2008 - by Ailsa Stevens 
Three independent studies have identified gene variants which contribute significantly to schizophrenia risk, taking steps towards understanding the cause of this highly complex condition which affects 1 in 100 people. Two of the three gene variants discovered were rare, but conferred 12 and 15 percent higher risks...
31 March 2008 - by Ailsa Stevens 
Two independent studies published in the journal Science this week suggest that many rare gene mutations may be responsible for causing schizophrenia, challenging the widely held theory that combinations of several relatively common mutations are to blame. The researchers found that very rare genetic disruptions, often unique...
5 November 2006 - by Dr Jess Buxton 
UK researchers have identified a genetic variation associated with an increased risk of schizophrenia in people with a strong family history of the condition. The team, based at Edinburgh University, discovered that individuals who inherit a particular version of the neuregulin (NRG1) gene have nearly three...
18 November 2005 - by BioNews 
Scottish researchers have identified another gene involved in schizophrenia and bipolar disorder (manic depression), a discovery that could lead to new drug treatments for the conditions. The team, based at the Universities of Edinburgh and Glasgow, has shown that an altered version of a gene called PDE4B is linked to...
24 October 2005 - by BioNews 
A new study provides more evidence that a gene which affects levels of a key brain chemical is involved in schizophrenia. A team based at Stanford University in California, US, found that children with a single, 'low-activity' copy of a gene called COMT are at higher risk of developing psychotic...
21 July 2003 - by BioNews 
How well people cope with stressful experiences such as divorce or unemployment is partly down to variations in a single gene, according to a new study by researchers based in the UK, US and New Zealand. The scientists, who published their findings in last week's Science, found that different versions...
4 June 2001 - by BioNews 
Scientists from the US National Institute of Mental Health (NIMH) have found a gene variation that may increase the risk of developing schizophrenia. The gene, called COMT (catecho-o-methytransferase) appears to control levels of the chemical dopamine in the brain. Lower levels of dopamine can affect performance in memory tasks and...
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