Schizophrenia involves some of the same genetic variations as autism and attention deficit disorders, a new whole-genome study has confirmed.

Schizophrenia, which affects about 1.5 percent of the U.S. population, can result in a variety of symptoms that include disrupted thinking, hallucinations, delusions and abnormal speech. The disease is thought to have genetic links but usually does not manifest itself until adolescence or early adulthood.

In an effort to assess some of the common genetic variations that might underpin this fairly common but thorny mental illness, researchers sequenced DNA from 1,735 adults with schizophrenia and 3,485 healthy adults. Across the patients that had the disease, the researchers found many frequent variations related to copying or deleting genes, known as copy-number variations. And among the genes that were more likely affected by these changes in schizophrenic individuals were CACNA1B and DOC2A, which help make proteins for calcium signals that regulate neurotransmitters in the brain. Two other relatively common variations, in RET and RIT2, would likely impact brain development.

"These genes affect synaptic function, so deletions or duplications in those genes may alter how brain circuits are formed," Hakon Hakonarson, director of the Center for Applied Genomics at The Children's Hospital of Philadelphia and coauthor of the new study, said in a prepared statement.

Previous research had turned up a few rare copy-number variations in schizophrenic patients, but they "explain only a small fraction of the genetic risk of this common complex disease," the researchers noted in their study, published online May 10 in Proceedings of the National Academy of Sciences. The new work confirmed higher rates of variations in some of the same networks disturbed in people with autism and attention deficit disorders.

"Although different brain regions may be affected in these different neuropsychiatric disorders, these overlaps suggest that there may be common features in their underlying pathogenesis," Hakonarson said.

Initial gene links for schizophrenia were reported nearly a decade ago, after researchers at Julius-Maximilian University of Würzburg in Germany found a common mutation on the 22nd chromosome in the protein-encoding gene WKL1. Since then, many studies have helped home in on triggers and therapies for the disease, but a cure for schizophrenia remains elusive.

"Much research remains to be done," Hakonarson said. But "detecting genes on specific pathways is a first step to identifying more specific targets for improved drug treatments."

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