March 24, 2005

Schizophrenia Genes and Cannabis

It was reported today by New Zealand researchers that a double dose of a faulty gene could be the connection between cannabis use and the development of schizophrenia, according to the New Scientist report.

In the original New Zealand study used by researchers, people who had smoked cannabis on three occasions by the age of 15 had a 10 per cent chance of developing the condition by the age of 26.

Dr Mary Cannon's research team recently re-analysed the data from from this study, adding another variable - genetic predisposition to schizophrenia.

The gene they investigated, called COMT (catechol-O-methyl transferase), encodes an enzyme that breaks down a signalling chemical dopamine in the brain.

COMT comes in two forms, one of which is marginally more common in people with schizophrenia and is thought to be a risk factor for the disease.

The results were crystal clear.

The team found that in New Zealanders with two copies of the "normal" version of COMT, smoking cannabis had little effect on their mental health. In people with one normal and one "bad" form of the gene, smoking cannabis slightly increased their risk of psychosis.

But for people with two copies of the bad gene, cannabis spelled trouble: smoking the drug as a teenager increased their likelihood of developing psychosis by a factor of 10.

For the full New Scientist Story See:

Early cannabis use may risk mental health

Original Research Journal Article: Moderation of the effect of adolescent-onset cannabis use on adult psychosis by a functional polymorphism in the catechol-O-methyltransferase gene: longitudinal evidence of a gene X environment interaction.

More information on Schizophrenia and Cannabis


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