APOE comes in three forms, or alleles, called 2, 3 and 4. The APOE-2 form of the gene increases the risk for Parkinson's cases that occur randomly, which is the most common form of Parkinson's. In a small number of cases, Parkinson's runs in families and is inherited. In Alzheimer's disease, the APOE-2 form of the gene is protective against the disease, and the APOE-4 form increases the risk of developing the disease.
The study analyzed all of the research on this topic, including a total of 22 studies with a total of 2,157 people with Parkinson's disease and 7,831 control subjects who did not have Parkinson's disease.
People with APOE-2 were 20 percent more likely to develop Parkinson's disease than people who had the other forms of the gene.
"This finding shows that APOE may have varying effects on different neurodegenerative disorders, and it underscores the importance of studying the relationship between genetic and environmental factors in the development of Parkinson's disease," said study author Xuemei Huang, MD, PhD, of the University of North Carolina in Chapel Hill.
Huang said the earlier studies had produced conflicting results, with most showing no significant association between APOE and Parkinson's disease.
"We hypothesized that any association would be too small to be detected or precisely estimated by a single study," Huang said. "By analyzing all of the studies together, we were able to determine that there is a link between APOE and Parkinson's."
The study was supported in part by grants from the National Institutes of Health and the National Institute of Environmental Health Sciences.
The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, autism and multiple sclerosis.
For more information about the American Academy of Neurology, visit its web site at www.aan.com/press/.
Editor's Notes: Dr. Huang will present this research during a scientific session at the 56th Annual Meeting at 2:45 p.m. PT (5:45 p.m. ET) on Tuesday, April 27 in Room 305 of the Moscone Convention Center. She will be available for media questions during a briefing at 11:00 a.m. PT (2:00 p.m. ET), Tuesday, April 27, in Room 214.