By Julie Steenhuysen

CHICAGO (Reuters) - A common gene that can cause abnormal heart rhythms can also trigger epileptic seizures in the brain and may explain the sudden, unexplained deaths that often occur in people with epilepsy, U.S. researchers said on Wednesday.

Testing epileptics for a mutation in this gene could give doctors the information they need to prevent some of these deaths, said Dr. Jeffrey Noebels of Baylor College of Medicine, whose study appears in the journal Science Translational Medicine.

Doctors have long known that patients with a mutation in the gene KvLQT1 -- which makes structures called ion channels that regulate electrical activity in the heart -- have a greater risk of sudden death from abnormal heart rhythms.

This gene also makes ion channels in brain cells, Noebels and colleagues found.

"We call it the missing link," Noebels said in a telephone interview. He believes the mutation in the brain triggers the seizure and may also trigger the heart disturbance, which in turn kills patients.

In patients with epilepsy, clusters of nerve cells called neurons in the brain send out the wrong signals, causing seizures. People with epilepsy are 23 times more likely to suddenly die from unexplained causes, but until now, doctors had no idea why, Noebels said.

"We hypothesized that if this same protein called an ion channel was in the brain, it could alter the way brain rhythms occur and trigger an epileptic seizure," Noebels said.

He said ion channels act like circuit breakers. "They regulate the way cells fire in electrical patterns."

The team used antibodies -- immune system proteins that home in on specific molecules -- to find the effects of the ion channel mutation in brain samples from mice and humans.

"We found it in the brain. That meant it could be the culprit in causing epilepsy," Noebels said.

They also measured heart rates and brain waves in mice that had been genetically engineered to have the human genetic mutations that make defective ion channels in the heart.

"We saw they were having electrical seizures in the brain that corresponded with heart rhythm disturbances," Noebels said. "We actually witnessed a death in a mouse that was due to the defective channel," he said.

Noebels said he suspects the defective gene is one of several that causes epileptic seizures.

"What this tells us is we need to encourage physicians to send patients to a cardiologist for an evaluation. They possess the tests for this class of genes to assess whether a patient is at increased risk for sudden death," he said.

In heart patients with this genetic defect, he said inexpensive drugs known as beta blockers and pacemakers can help regulate dangerous heartbeats.

(Editing by Maggie Fox and Todd Eastham)

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