Washington, July 4 Schizophrenia and bipolar disorder share genetic roots that seem to be specific to serious mental disorders, new studies have revealed.

A trio of genome-wide studies, collectively the largest to date, has pinpointed a vast array of genetic variations that cumulatively may account for at least a third of the genetic risk for schizophrenia.

One of the studies traced schizophrenia and bipolar disorder, in part, to the same chromosomal neighbourhoods.

“These new results recommend a fresh look at our diagnostic categories,” said Thomas R. Insel, director of the National Institute of Mental Health (NIMH), part of the National Institutes of Health.

“If some of the same genetic risks underlie schizophrenia and bipolar disorder, perhaps these disorders originate from some common vulnerability in brain development.”

The trio of studies, the SGENE, International Schizophrenia (ISC) and Molecular Genetics of Schizophrenia (MGS) consortia shared their results – making possible meta-analyses of a combined sample totalling 8,014 cases and 19,090 controls.

All three studies implicate an area of Chromosome 6 (6p22.1), which is known to harbour genes involved in immunity and controlling how and when genes turn on and off.

This hotspot of association might help to explain how environmental factors affect risk for schizophrenia.

For example, there are hints of auto-immune involvement in schizophrenia, such as evidence that offspring of mothers with influenza while pregnant have a higher risk of developing the illness, said a NIMH release.

“Our study was unique in employing a new way of detecting the molecular signatures of genetic variations with very small effects on potential schizophrenia risk,” explained Pamela Sklar of the Harvard University and the Stanley Centre for Psychiatric Research, who co-led the ISC team with Shaun Purcell.

“Individually, these common variants’ effects do not all rise to statistical significance, but cumulatively they play a major role, accounting for at least one third – and probably much more – of disease risk,” said Purcell.

These three reports, each funded in part by NIMH, appeared in the July 1 edition of Nature.