July 1 (Bloomberg) -- Common variations in genes may underlie schizophrenia, the mental illness known to run in families for more than 100 years, with no one single variation conferring the majority of risk, three studies show.

The research gives scientists a map of the disorder’s biology, which may lead to understanding schizophrenia’s mechanism, said Pamela Sklar, a geneticist and psychiatrist at Massachusetts General Hospital in Boston, who led one of the teams publishing reports today in the journal Nature.

Recent discoveries explain about 30 percent of genes’ contributions to schizophrenia, said Thomas Lehner, the chief of the National Institutes of Mental Health’s genomics research branch, in a statement today. Even if one specific mutation isn’t identified as accounting for the majority of the risk, the findings may give doctors clues for drug targets, said David Collier, a professor at King’s College London.

“We hope that this will help us understand pathways that will allow us to better treat patients,” said Collier, an author on one of the other studies, in a press briefing.

Most people with schizophrenia take antipsychotic drugs, such as Eli Lilly & Co.’s Zyprexa, Johnson & Johnson’s Risperdal, and Pfizer Inc.’s Geodon, or older, generic medicines such as haloperidol. These drugs help control severe symptoms, such as hearing voices or violent outbursts. They also can produce side effects such as weight gain, diabetes, and movement disorders.

‘Partially Effective’

“While we have some partially effective treatments, we don’t have anything fully effective yet,” Sklar said. The discoveries reported today may help researchers develop drugs based on what causes the disease, she said.

Many of the genes were involved in generating new brain cells and maintaining the synapses, gaps between neurons that allow the cells to communicate, Collier said.

All three studies identified an area on chromosome six, which controls the activation of other genes and is also in charge of immunity. The area may explain 2005 reports from Columbia University in New York and the University of Vermont in Burlington suggesting that pregnant mothers with influenza, which may reflect or affect the immune system, are likelier to have children with schizophrenia.

A third study, led by scientists from deCode Genetics Inc., based in Reykjavik, Iceland, analyzed the genomes of more than 50,000 patients from 14 countries. That study found variants in the transcription factor 4 gene on chromosome 18, which helps guide brain development, and on chromosome 11, near the neurogranin gene, which helps regulate memory and thought processes.

Research published in Nature last year also found schizophrenia to be linked to spontaneous defects in DNA where genes are duplicated or deleted in random processes. Those defects aren’t necessarily inherited from parents.

To contact the reporter on this story: Elizabeth Lopatto in New York at elopatto@bloomberg.net.

Last Updated: July 1, 2009 13:00 EDT