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Researchers Zero In on Genetic Link to Parkinson's

Posted on: Monday, 17 January 2005, 21:00 CST

MONDAY, Jan. 17 (HealthDayNews) -- Scientists have found the first evidence of a genetic mutation that would be the most common genetic cause of Parkinson's disease identified thus far.

The mutation, in the LRRK2 gene, may be responsible for up to 5 percent of cases of Parkinson's in people with a family history of the disease, and 1.5 percent to 2 percent of cases in individuals without a family history.

Genetic testing for this particular mutation may be available in as little as one year, said study co-author Andrew Singleton, chief of the molecular genetics unit at the Laboratory of Neurogenetics at the National Institute on Aging. Actual therapies, however, will take much longer to develop, he added.

"The whole idea of this kind of research is to get a handle on the chain of events that cause disease," Singleton said. "Once you get a handle, you can try to interrupt the pathway. All of the therapies for Parkinson's right now are aimed at alleviating symptoms. The whole idea is to provide a cure or to prevent the disease. In terms of understanding the disease, it's a step forward. I think we're really getting somewhere."

The findings are published in two papers appearing online Jan. 18 in The Lancet.

Parkinson's disease affects at least half a million people in the United States, and possibly many more, and is the second most common neurodegenerative disease after Alzheimer's. About 1 percent of people over the age of 65 and 3 percent of people over the age of 75 are affected by the disease. It is marked by the degeneration of nerve cells in the area of the brain that controls movement, resulting in tremors, stiffness, slowness of movement, and impaired balance and coordination.

For a long time, scientists had thought the cause of Parkinson's was environmental, but more recently they have acknowledged it is likely a result of an interplay of factors. "We are understanding more and more that it is probably a mix of environment and genetics," Singleton said.

Four or five genes have already been implicated in Parkinson's but only in a rare form of the disease that affects those with a family history.

For the familial part of the new research, Singleton and his colleagues looked at 767 people with Parkinson's disease from 358 families. Of these individuals, 5 percent had the genetic mutation.

The researchers also assessed 482 Parkinson's patients who did not have a family history of the disease. The mutation was present in 1.6 percent of these people.

A mutation in just one copy of the gene can cause the disease, the researchers said.

The LRRK2 gene encodes a protein named dardarin, from the Basque word dardara, meaning tremor. It's not entirely clear how the gene works, Singleton said.

"We don't know what the gene does. We only found it two or three months ago," he said. "One would suspect that it alters kinase function but we don't know if it activates it or deactivates it." A kinase is like a switch that turns proteins on and off.

The next step is to find out how the mutation actually works so therapies can be devised.

The most immediate effect of the research, Singleton said, will be in genetic counseling: "This is something clinicians will talk to patients about."

Even though 1 percent and 5 percent may not sound high, Singleton said the percentages uncovered by the new studies were actually much higher than he had expected.

"When you think perhaps there are a million people with Parkinson's in the U.S. and you find a mutation for 2 percent, that's 20,000 people. That's pretty considerable," he said.

More information

To learn more about the disease, visit the National Parkinson Foundation.

SOURCES: Andrew Singleton, Ph.D., chief, molecular genetics unit, Laboratory of Neurogenetics, National Institute on Aging, Bethesda, Md.; Jan. 18, 2005, The Lancet online~PARK~~GENT~

Source: HealthSCOUT

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