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A team of researchers has discovered new evidence that Parkinson's disease may 
have an infectious or autoimmune origin. "Common genetic variation in the HLA 
region is associated with late-onset sporadic Parkinson's disease" appears 
online in Nature Genetics.

The study was conducted by the NeuroGenetics Research Consortium, an 
international team of researchers led by Haydeh Payami, research scientist at 
the New York State Department of Health Wadsworth Center. The clinical 
directors for the study were Dr. Cyrus Zabetian, associate professor of 
neurology at the University of Washington and VA Puget Sound Health Care 
System, Stewart Factor at Emory University and John Nutt at Oregon Health and 
Sciences University.

The research team studied more than 2,000 Parkinson's disease patients and 
2,000 healthy volunteers from clinics in Oregon, Washington, New York and 
Georgia, assessing clinical, genetic and environmental factors that might 
contribute to the development and progression of Parkinson's disease and its 
complications. Some of the research subjects were tracked for nearly two 
decades.

"Over the years, there have been subtle hints that immune function might be 
linked to Parkinson's disease" said Zabetian. "But now we have much more 
convincing evidence of this and a better idea of which parts of the immune 
system might be involved."

In the study, researchers detected a new association with the HLA (human 
leukocyte antigen) region, which contains a large number of genes related to 
immune system function in humans. With the new findings, and link to HLA, 
researchers will now be encouraged to take a fresh look at the possible role 
of infections, inflammation and autoimmunity in Parkinson's disease.

HLA genes are essential for recognizing foreign invaders from the body's own 
tissues. Similarly, HLA molecules are supposed to recognize a body's own 
tissue as itself and prevent immune reactions against them. But the system 
doesn't always work perfectly. HLA genes are highly variable from individual 
to individual. Certain variants of the genes are associated with increased 
risk or protection against infectious disease, while other variants can induce 
autoimmune disorders in which the immune system attacks the body's own 
tissues. Multiple sclerosis, a neurological disease caused by autoimmunity, is 
also associated with HLA-DR. The genetic variant that is associated with 
Parkinson's disease is in the same region as the one associated with multiple 
sclerosis.

People who take non-steroidal anti-inflammatory drugs (NSAIDs, such as 
ibuprofen) have a reduced risk of developing Parkinson's disease, which also 
supports an immune-related mechanism. The protective effect of NSAIDs is not 
the same for everyone, likely because of genetic differences, and NSAIDs can 
have side effects. Pursuing the connection between Parkinson's disease and 
inflammation, especially in the context of variable genetic makeup, may lead to 
better, more selective drugs for treating Parkinson's disease.

Consortium leaders recognize the study would not have been possible without 
the precious help from volunteer patients. "This type of research could not be 
done if it weren't for the willing and dedicated individuals who volunteer as 
research subjects," said Payami, who acknowledged that some study subjects 
participated for nearly two decades.

What's next for the team? "Our results also pointed to several other genes 
that might play a role in developing Parkinson's disease, and these findings 
need to be confirmed, so we have a lot of work ahead of us" said Zabetian. He 
and others in the consortium will now mine the data even more for gene-
environment interactions, with a goal of finding environmental triggers and 
protectors to develop genetically-personalized therapeutics for treatment and 
prevention of Parkinson's disease.


Source: University of Washington

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