The researchers also found that the APOE-4 form of the gene, which has long been linked to an increased risk of Alzheimer's disease, is not a risk factor in Parkinson's disease.
A report of the findings appears this week in the June issue of the journal Neurology.
"It basically shows that neurodegenerative diseases may differ in significant risk factors, contrary to prevailing views," said lead author Dr. Xuemei Huang, assistant professor of neurology in UNC's School of Medicine.
The gene APOE refers to apoliprotein E, which takes three forms, or alleles: APOE-2, -3 and -4. These and other APO genes transcribe apolipoproteins, protein particles involved in lipid metabolism that shuttle these fatty acids, including cholesterol, through the body. "APOE-4 is a major susceptibility gene for sporadic and familial Alzheimer's disease and has been associated with poor clinical outcome in people with acute head injury and stroke," Huang said. "In the brain, apolipoprotein E-4 may be involved in neuron repair and in the removal of dead cells, so if you have APOE-4, you may be at higher risk of Alzheimer's disease or poor recovery from stroke and brain injury."
On the other hand, APOE-2 seems to occur with lower frequency in people with Alzheimer's disease and is linked with late onset of that disease's symptoms. The APOE type is linked to longevity and is more likely to be found in centenarians, she added. Thus, APOE-4 was perceived as the "bad guy" in neurological diseases, while APOE-2 was thought the "good guy."
"Although most people in the field believed this, the results of individual studies generally