Scientists have found 30,000 different gene variations which suggest that schizophrenia is much more complex than previously thought, and can arise not only from rare genetic variants, but common ones as well.

The DNA of 10,000 people with schizophrenia, and 20,000 without was examined by a multinational group of researchers from the International Schizophrenia Consortium, the Molecular Genetics of Schizophrenia consortium and SGENE in three separate studies.
 
The researchers found 30,000 common gene variations linked with the mental illness which together could account for more than a third of the inherited risk of schizophrenia. They also showed the condition is genetically similar to bipolar disorder also known as manic depression and said quick tests to predict either disease is a long way off.
 
Mick O'Donovan of London's Institute of Psychiatry, who worked on one of the studies said, "It's like we've got a 'join-the-dots picture', and we now know we have several thousands of dots to be joined. But we don't even have numbers on them yet so we don't know in what order to connect them up."
 
The researchers said the findings suggested that schizophrenia is much more complex than previously thought, and can arise not only from rare genetic variants, but common ones as well. Although the cause of schizophrenia remains unclear, it is thought that up to 90% of cases may be inherited.
 
Working together under the International Schizophrenia Consortium, the scientists, found the same genetic patterns linked to bipolar disorder, which the researchers said was significant as it adds to recent evidence challenging previous thinking that the two disorders were distinct.
 
Kari Stefansson, chief executive of Decode Genetics of Iceland, who worked on one of the studies said, "Discoveries such as these are crucial for teasing out the biology of the disease making it possible for us to begin to develop drugs targeting the underlying causes and not just the symptoms of the disease."
 
Published in the journal Nature, all three studies highlight genes found on Chromosome 6 in area known as the Major Histocompatibility Complex, which plays a role in the immune system, and in controlling when other genes are switched on and off. This might help explain why environmental factors also seem to affect risk for schizophrenia feel the researchers.
 
The researchers identified 30,000 tiny genetic variants more common in people with schizophrenia and a similar pattern was found in people with bipolar disorder showing a possible overlap between the two conditions.
 
Dr Thomas Insel, of the US National Institute of Mental Health said, "These new results recommend a fresh look at our diagnostic categories.
 
"If some of the same genetic risks underlie schizophrenia and bipolar disorder, perhaps these disorders originate from some common vulnerability in brain development."

The researchers said that more work is needed to establish exactly how the genetic variants translate into schizophrenia. Researcher Dr Pamela Sklar, of Massachusetts General Hospital said, "We fully expect that future work will assemble them into meaningful pathways that will teach us about the biology of schizophrenia."