Schizophrenia, Bipolar May Share Cause

Both Mental Illnesses Linked to Problem With Genes That Make Nerve Coating

From the WebMD Archives

Sept. 4, 2003 -- New research offers compelling evidence that the mental illnesses schizophrenia and bipolar disorder have a common genetic cause. The findings could eventually lead to better treatments for these and other diseases of the brain, researchers say.

The researchers used newly available, highly sensitive, molecular testing techniques to examine the postmortem brains of 15 people with schizophrenia, 15 people with bipolar disorder, and 15 people with neither illness. They found that the genes responsible for producing the protective coating around nerves in the brains of the people with the mental illnesses were less active than normal.

This protective coating around nerves -- called myelin -- insulates the nerves and aids the transmission of signals from the brain to the rest of the body.

Several previous studies have shown abnormalities in genes responsible for myelin production in the brains of people with schizophrenia, but this research is the first to identify similar abnormalities in the brains of people with bipolar disorder (previously called manic depression).

Researcher Sabine Bahn, MD, PhD, and colleagues from Cambridge, England's Babraham Institute found a high degree of overlap in gene activity between the brains of people with schizophrenia and bipolar disorder. Their findings are reported in the Sept. 5 issue of The Lancet.

Don't Blame Dopamine

Bahn tells WebMD that her research and the earlier myelin findings argue against the widely held theory that schizophrenia and similar disorders are caused by the brain's overproduction of the brain chemical dopamine.

"The dopamine hypothesis has been studied for the last 20 years, but nothing concrete has been proven," she says. "We are not saying that a myelin hypothesis should replace the dopamine hypothesis, but, rather, that we should all just take a step back and see what these new technologies tell us."

Mount Sinai School of Medicine psychiatry and biological chemistry Professor Kenneth L. Davis, MD, who led one of the first research teams to link underactive myelin genes to schizophrenia, says the research has prompted a sea change in the thinking about the cause of mental illness.

Schizophrenia is a disease that everyone thought was related to nerve cells and signal transmission, not myelin, he tells WebMD. Researchers now know that myelin genes are less active in schizophrenia and bipolar disorder. What they need to find out is what these genes do and why they are less active, he says.

The long-range hope, Davis says, is that answering these questions will eventually lead to better treatments for schizophrenia, bipolar disorder, and other mental illnesses.

"If we can figure out what these genes do and why they are [underactive] then maybe we can develop new targets for drug development," he says. "Right now there is no obvious drug target that comes from this work, but as this research evolves new targets could arise."

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SOURCES: The Lancet, Sept. 5, 2003; vol 362: pp 798-805. Sabine Bahn, MD, PhD, department of neurobiology, Babraham Institute, Cambridge, England. Kenneth L. Davis, MD, professor of psychiatry, pharmacology, and biological chemistry, Mount Sinai School of Medicine, New York.
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