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International study reveals thousands of genetic contributions to schizophrenia and bipolar

01 July 2009

Scientists from the MRC Centre for Neuropsychiatric Genetics and Genomics at Cardiff University working as part of an international research team have discovered that most of the genetic basis of schizophrenia comes from the accumulation of small effects from thousands of common genetic variants. Many of these genetic effects are also shared by individuals with bipolar disorder.

In a novel use of genome chip data, the International Schizophrenia Consortium found thousands of genetic variants had small influences separately but together make a strong impact on a person’s risk for developing schizophrenia and bipolar disorder, in a report published online today by the journal Nature.

Michael O'Donovan, Professor of Psychiatric Genetics at the MRC Centre for Neuropsychiatric Genetics and Genomics said: "The very large number of genetic contributions surprised us initially yet we observed the same pattern across multiple samples, making us confident that we were measuring something real and relevant."

Schizophrenia is a common, chronic and often devastating brain disorder characterised by persistent delusions and hallucinations. It affects about 1 person in 100 and usually strikes in late adolescence or early adulthood.

Despite the availability of effective treatments, the course of the illness is usually chronic and response to treatments is often limited, leading to prolonged disability and personal suffering. Family history, which signifies genetic inheritance, is a strong risk factor for schizophrenia and bipolar disorder. Last year, the International Schizophrenia Consortium found that rare chromosomal deletions and duplications of all types elevate risk of developing schizophrenia.

Formed in 2006, the International Schizophrenia Consortium is led by senior researchers from 11 institutes in Europe and the USA. Crucial to the success of the project was the willingness of Consortium groups to pool DNA resources that have taken them years to collect, totaling 3,391 individuals with schizophrenia and 3,181 related individuals without the disorder.

The investigators used new genomic technologies and novel analytical techniques. Based upon the theoretical models of Consortium members Drs. Naomi Wray and Peter Visscher (Queensland Institute of Medical Research, Brisbane, Australia), the Consortium tested hundreds of thousands of genetic variants to find those more common in patients with schizophrenia than in people without the disorder.

They then went on to test a subset of about 30,000 of these variants in additional people with schizophrenia and also in people with bipolar disorder. The critical finding was that the same large group of genetic variants was found in the new samples of schizophrenia patients, even when they were collected by many different investigators and tested in different laboratories.

Surprisingly, this group of schizophrenia-related variants was also more common in people with bipolar disorder. These results are at odds with the orthodoxy in psychiatry that the two disorders are distinct, The finding was relatively specific to psychiatric disorders rather than general illness, since the variants were not found in excess in people with a range of other diseases such as diabetes and heart disease.

Eric Lander, founding director of Consortium partner The Broad Institute, and a member of the President Obama’s Council of Advisors on Science and Technology said: "Over the past year, using techniques designed to study common DNA changes, psychiatric disease geneticists have detected more statistically compelling findings than in the previous 100 years."

Dr Thomas Insel, director of the National Institute for Mental Health, which partially funded the study, said:" If some of the same genetic risks underlie schizophrenia and bipolar disorder, perhaps these disorders originate from some common vulnerability in brain development. Of course the big question then is how some people develop schizophrenia and others develop bipolar disorder."

Professor Ian Hickie, Executive Director of the Brain and Mind Institute, University of Sydney, Australia said: "This is a key study from both a conceptual and a practical perspective. It provides striking evidence for the common genetic risk factors for the major psychiatric disorders. We are well on the way to dismantling the century-old classification systems in psychiatry that have proved to be poor representations of the underlying biology."

The study was supported by grants from the Medical Research Council, Wellcome Trust, Science Foundation Ireland, Stanley Medical Research Foundation, the National Institute of Mental Health and the Sylvan Herman Foundation.

Cardiff University

Cardiff University is recognised in independent government assessments as one of Britain’s leading teaching and research universities and is a member of the Russell Group of the UK’s most research intensive universities. Among its academic staff are two Nobel Laureates, including the winner of the 2007 Nobel Prize for Medicine, Professor Sir Martin Evans. Founded by Royal Charter in 1883, today the University combines impressive modern facilities and a dynamic approach to teaching and research. The University’s breadth of expertise in research and research-led teaching encompasses: the humanities; the natural, physical, health, life and social sciences; engineering and technology; preparation for a wide range of professions; and a longstanding commitment to lifelong learning. In the recent independent UK Research Assessment Exercise, almost 60 per cent of University research was assessed as either world-leading or internationally excellent. In Neuroscience, Psychiatry and Psychology, 80 per cent was either world-leading or internationally excellent, placing Cardiff joint first in the UK in this field.

Visit the University website at: www.cardiff.ac.uk

About the Medical Research Council

The Medical Research Council is dedicated to improving human health through excellent science. It invests on behalf of the UK taxpayer. The results have led to some of the most significant discoveries in medical science and benefited the health and wealth of millions of people in the UK and around the world. Research ranges from molecular level science to public health research, carried out in universities, hospitals and a network of MRC units and institutes. The MRC liaises with the Health Departments, the National Health Service and industry to take account of the public’s needs. www.mrc.ac.uk

To arrange an interview with Professor O’Donovan, please contact Steve Pogonowski in the MRC Press Office on 0207 670 5139 or stephen.pogonowski@headoffice.mrc.ac.uk

For further information about Cardiff University please contact:

Lowri Jones, Public Relations Office, Cardiff University. 029 2087 0995 or e-mail: JonesLC3@cardiff.ac.uk