WEDNESDAY, Oct. 21 (HealthDay News) -- An unprecedented worldwide study has clinched the case that the gene behind Gaucher disease, a rare neurological disorder, is also involved in Parkinson's disease.

"For those of us who work with rare disorders, it is heartwarming to come up with insights that are applicable to more common disorders," said Dr. Ellen Sidransky, a senior investigator in the U.S. National Human Genome Research Institute, and leader of a study reported in the Oct. 22 issue of the New England Journal of Medicine.

Gaucher disease affects no more than one in 100,000 people in most populations, with an estimated 5,400 cases in the United States. As many as 3 million to 4 million Americans are estimated to have Parkinson's disease.

Gaucher disease develops in people who have two defective copies of a gene designated GBA. It codes for production of an enzyme that breaks down glucocerebrosidase, a fatty substance normally found in the body. The faulty gene allows accumulation of the substance, which can harm the spleen, liver, lungs, bone marrow and even the brain.

Discovery that the two conditions have a common genetic element cannot be applied immediately to relieve the stiffness, trembling and other symptoms of Parkinson's disease, Sidransky said.

"We have to be cautious about jumping into clinical applications," she said. "This gene plays a more common role in Parkinson's than other genes, but it is not necessarily predictive of Parkinson's disease. It is a risk factor rather than a gene that predicts the disease."

"The work will teach us about the mechanisms of Parkinson's disease, and once we understand the mechanisms we can come up with therapies that can help patients with Parkinson's disease. And it could ultimately lead to better therapies that could help patients with Gaucher disease," Sidransky said.

Several smaller studies have suggested the genetic link between the two conditions, "but there have always been questions based on their size and controls," Sidransky said. "Once and for all, we have put together a large enough number so that no one will question the results."

The study she led involved 16 institutions around the world. A listing of the institutions and researchers filled a complete page on the journal in fine print.

Those researchers examined the frequency of GBA variants in 5,691 people with Parkinson's disease, including 780 Ashkenazi Jews, an ethnic group in which Gaucher disease is more common. Their data was matched with genetic information from 4,898 disease-free individuals, including 387 Ashkenazi Jews.

At least one of two common GBA variants was found in 3.2 percent of the people with Parkinson's disease, but only 0.6 percent of the disease-free individuals. Among the Ashkenazi participants, 15.3 percent of those with Parkinson's disease carried a GBA variant, compared to 3.4 percent of disease-free Ashkenazi individuals.

In addition to increasing the risk of Parkinson's disease, presence of a GBA variant was associated with early onset of the condition, four to five years sooner than ordinarily seen, the study found.

"Its importance is that it may indicate a new pathway to explore for the etiology [cause] of Parkinson's disease, and ultimately a target for drug discovery," said Dr. Karen Marder, a professor of neurology at Columbia University Medical Center, and one of the researchers in the trial.

The discovery raises some possible issues about genetic counseling, Marder said, but more work must be done before that can influence medical practice.

"This is among the most important susceptibility factors for Parkinson's that has ever been discovered, but it is premature to talk about using it in clinical practice," she said.

More information

Symptoms and treatment of Parkinson's disease are described by the U.S. National Institute of Neurological Disorders and Stroke.

SOURCES: Ellen Sidransky, M.D., senior investigator, U.S. National Human Genome Research Institute, Bethesda, Md.; Karen Marder, M.D., professor, neurology, Columbia University Medical Center, New York City; Oct. 22, 2009, New England Journal of Medicine

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