July 1 (HealthDay News) -- Immune function may play a role in schizophrenia, say scientists who found that schizophrenia patients have genetic variations on a section of chromosome 6 that contains numerous genes associated with immune response.

That region of the human genome has not previously been suspected as a risk factor for schizophrenia, which affects about 1 in 100 people. It was already known that genetics account for about 80 percent of risk for schizophrenia. Most cases of the mental health disorder are believed to be caused by interactions between a large number of genes.

"That makes it hard to tease out, in a statistically significant way, any of these schizophrenia-associated genes," Dr. Douglas Levinson, director of the Program on the Genetics of Brain Function at Stanford University School of Medicine, said in a news release from the university.

But studying a large number of people can reveal that information, so Levinson and colleagues analyzed DNA data from three studies that included 27,000 people -- 8,000 with schizophrenia and 19,000 people without the disease.

The study participants were restricted to those of European ancestry. This was done in order to exclude numerous non-disease-related genetic differences that would have to be sorted through if participants had different ancestries.

The researchers used the latest genetic technologies to search for tiny genetic variations called single base-pair polymorphisms (SNPs). They found that the largest genetic differences between people with schizophrenia and those without the disease were found on chromosome 6.

The findings are presented in three papers published online July 1 in the journal Nature. "The papers present the first highly significant findings of gene regions associated with schizophrenia risk," Levinson said.

He added that "these findings show that our genetic methods are working and that the genetic underpinnings of schizophrenia can be understood. Similar methods have produced critical new discoveries in many other common diseases, once very large numbers of people could be studied. Now we see that the same approach works for psychiatric disorders like schizophrenia."

SOURCE: Stanford University School of Medicine, news release, July 1, 2009