People who carry the gene for a rare genetic problem known as Gaucher disease have at least five times the normal risk of developing Parkinson's disease, researchers reported today in the New England Journal of Medicine. Some clinicians had noticed an apparent link between the two conditions in the past, but a new international study of nearly 5,700 people is the first to show the magnitude of the risk. The finding suggests that the gene is one cause of the disease, but indicates that other factors must be operating as well because not all patients who have Gaucher also develop Parkinson's.
Gaucher disease, which afflicts an estimated 5,400 Americans, is caused by defects in the gene known as GBA, which serves as the blueprint for the production of an enzyme known as glucocerebrosidase. The enzyme breaks down a fatty substance called glucocerebroside which, when not disposed of, can harm the spleen, liver, lungs, bone marrow and, in some cases, the brain. People with two defective genes suffer from the disease, which comes in three distinct types. Lifespan may range from as little as 2 years to as many as 40 or 50.
People with only one defective gene do not suffer from symptoms and are said to be carriers. About one in 100 Americans carries the gene, but among certain groups, like Ashkenazi Jews, the incidence rises to one in 15. It was previously thought that the gene was harmless in such people, but the new results show that is not the case.
Dr. Ellen Sidransky of the National Human Genome Research Institute had been intrigued by an observed link between Gaucher and Parkinson's. To explore it, she organized a consortium of 64 researchers at 16 institutions worldwide--virtually every Gaucher researcher in the world. They studied two common GBA variants in 5,691 people with Parkinson's disease, including 780 Ashkenazi Jews, and compared them to 4,898 disease-free individuals, including 387 Ashkenazi Jews.
They found that 3.2% of the Parkinson's patients had at least one of the common variants, compared with only 0.6% of the healthy people, a five-fold increase. Among the Jews, 15.3% of those with Parkinson's carried the gene, compared with 3.4% of healthy Jews.
Five of the research centers sequenced the entire GBA gene in 1,642 non-Ashkenazi Parkinson's patients and 609 health non-Ashenazis, looking for other mutations. They found mutant genes in 7% of the patients, indicating that their risk of developing Parkinson's was 10 times normal.
The finding does not offer any new ideas about how to treat Parkinson's disease. Indeed, researchers are currently at a loss to explain the mechanism by which the defective gene increases the risk of Parkinsonism, which affects an estimated 3 million to 4 million Americans. But they hope that exploring the link will provide new information about how the disease develops and progresses.
-- Thomas H. Maugh II