Genes that increase the risk of developing schizophrenia may also increase the likelihood of using cannabis, according to a new study led by King's College London, published today in Molecular Psychiatry.
Previous studies have identified a link between cannabis use and schizophrenia, but it has remained unclear whether this association is due to cannabis directly increasing the risk of the disorder.
The new results suggest that part of this association is due to common genes, but do not rule out a causal relationship between cannabis use and schizophrenia risk.
The study is a collaboration between King's and the Queensland Institute of Medical Research in Australia, partly funded by the UK Medical Research Council (MRC).
Mr Robert Power, lead author from the Institute of Psychiatry at King's, says: "Studies have consistently shown a link between cannabis use and schizophrenia. We wanted to explore whether this is because of a direct cause and effect, or whether there may be shared genes which predispose individuals to both cannabis use and schizophrenia."
Cannabis is the most widely used illicit drug in the world, and its use is higher amongst people with schizophrenia than in the general population. Schizophrenia affects approximately 1 in 100 people and people who use cannabis are about twice as likely to develop the disorder. The most common symptoms of schizophrenia are delusions (false beliefs) and auditory hallucinations (hearing voices). Whilst the exact cause is unknown, a combination of physical, genetic, psychological and environmental factors can make people more likely to develop the disorder.
Previous studies have identified a number of genetic risk variants associated with schizophrenia, each of these slightly increasing an individual's risk of developing the disorder.
The new study included 2,082 healthy individuals of whom 1,011 had used cannabis. Each individual's 'genetic risk profile' was measured - that is, the number of genes related to schizophrenia each individual carried.
The researchers found that people genetically pre-disposed to schizophrenia were more likely to use cannabis, and use it in greater quantities than those who did not possess schizophrenia risk genes.
Power says: "We know that cannabis increases the risk of schizophrenia. Our study certainly does not rule this out, but it suggests that there is likely to be an association in the other direction as well - that a pre-disposition to schizophrenia also increases your likelihood of cannabis use."
"Our study highlights the complex interactions between genes and environments when we talk about cannabis as a risk factor for schizophrenia. Certain environmental risks, such as cannabis use, may be more likely given an individual's innate behaviour and personality, itself influenced by their genetic make-up. This is an important finding to consider when calculating the economic and health impact of cannabis."
For a copy of the paper, or interview with the author, please contact Seil Collins, Press Officer, Institute of Psychiatry, King's College London firstname.lastname@example.org / (+44) 0207 848 5377 / (+44) 07718 697 176
Additional funding was provided by the National Institutes of Health, Australian National health and Medical Research Council, Australian Research Council, GenomEUtwin Project, Centre for Research Excellence on Suicide Prevention in Australia, the National Institute for Health Research Biomedical Research Centre (NIHR BRC) at the South London and Maudsley NHS Foundation Trust and King's College London and the Netherlands Organization for Health Research and Development.
Paper reference: Power, R. et al. 'Genetic predisposition to schizophrenia associated with increased use of cannabis' published in Molecular Psychiatry.
About King's College London
King's College London is one of the top 20 universities in the world (2013/14 QS World University Rankings) and the fourth oldest in England. It is The Sunday Times 'Best University for Graduate Employment 2012/13'. A research-led university based in the heart of London, King's has more than 25,000 students (of whom more than 10,000 are graduate students) from nearly 140 countries, and more than 6,500 employees. King's is in the second phase of a £1 billion redevelopment programme which is transforming its estate.
King's has an outstanding reputation for providing world-class teaching and cutting-edge research. In the 2008 Research Assessment Exercise for British universities, 23 departments were ranked in the top quartile of British universities; over half of our academic staff work in departments that are in the top 10 per cent in the UK in their field and can thus be classed as world leading. The College is in the top seven UK universities for research earnings and has an overall annual income of nearly £554 million.
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