New research has suggested that a virus that has typically been thought of as common and harmless may actually be associated with an increased risk of Parkinson's disease. This study, which has been reported in JCI Insight, found evidence of this virus, known as human pegivirus (HPgV), in half of the post-mortem brains Parkinson's patients, while it was not found in similar samples from unaffected individuals.
"HPgV is a common, symptomless infection previously not known to frequently infect the brain," said senior study author Dr. Igor Koralnik, chief of neuroinfectious diseases and global neurology at Northwestern Medicine in Chicago.. "We were surprised to find it in the brains of Parkinson's patients at such high frequency and not in the controls."
The scientists also noted that HPgV seems to trigger different immune responses in different people, and those responses depend on a person's genetic makeup. This may indicate that the virus is an environmental influence that could have a variety of impacts on immunity, some of which have not been recognized before. It might also be affecting the development of Parkinson's, particularly in individuals with certain genetic characteristics or variations.
Parkinson's is becoming more common, and while some cases are linked to genetics, others could have much more to do with environmental factors. Exposure to dry cleaning chemicals, for example, is one environmental influence that could be increasing certain people's risk. But the degree of that risk may also depend on small changes in a person's DNA, some of which are common while others are more rare.
Parkinson's disease is known to arise when dopamine-generating hormones die off, leading to movement disorders and other problems with balance and coordination.
This study, which analyzed a small group of ten post-mortem Parkinson patient brains and fourteen unaffected individuals, showed that HPgV was idenitfiable in the brains of five of the Parkinson's patients. None of the unaffected people carried the virus.
There was also visible brain damage in patients who carried HPgV infections.
The investigators also looked for HPgV in the blood samples of Parkinson's patients, but only about 1% of the 1,000 samples were positive for the virus.
However, the individuals who were infected with detectable HPgV also showed signs of a different immune response to the infection. This was notable for people who carried mutations in a gene called LRRK2.
"We plan to look more closely at how genes like LRRK2 affect the body's response to other viral infections to figure out if this is a special effect of HPgV or a broader response to viruses," said Koralnik. "One big question we still need to answer is how often the virus gets into the brains of people with or without Parkinson's. We also aim to understand how viruses and genes interact; insights that could reveal how Parkinson's begins and could help guide future therapies."
Sources: Medical Express, JCI Insight