New Findings on Virus and Parkinson’s Disease

Researchers have found notably elevated levels of a common virus in the brains of individuals with Parkinson’s disease, which could indicate a potential factor behind the disorder.

A team from Northwestern Medicine studied brain samples from both Parkinson’s patients and those without the disease. They discovered traces of the human pegavirus (HPgV) in 50% of the brains affected by Parkinson’s, while none were found in the control group.

Patients carrying the virus exhibited unique immune responses and marked brain alterations, which seemed further complicated by genetic factors. Parkinson’s disease typically worsens over time, damaging the brain’s dopamine-producing areas and leading to symptoms like tremors, rigidity, and difficulties in movement.

Interestingly, those with the virus present in their brains demonstrated more severe brain damage. Additionally, patients with HPgV in their bloodstream had indications that their cells were having trouble generating energy and clearing out cellular debris.

HPgV, transmitted through blood, is closely related to the Hepatitis C virus. However, it was previously assumed to be harmless, often lying inactive in the body. This new research calls that belief into question, hinting at a possible connection to Parkinson’s.

Dr. Igor Koralnik, leading the neuroinfectious diseases department at Northwestern Medicine, remarked that these findings suggest that a virus previously thought to be benign may actually have significant effects, particularly concerning how Parkinson’s might develop in individuals with certain genetic makeups.

The exact origin of Parkinson’s remains elusive, impacting around one million Americans and leading to mobility and cognitive issues. Researchers have been exploring various contributing factors, including viruses, for quite some time.

When the brain notices a virus, it often initiates inflammation as a defensive response. While this reaction aims to combat the infection, prolonged or excessive inflammation can inadvertently harm sensitive brain cells, notably the dopamine-producing neurons that are affected in Parkinson’s.

In their blood analysis, researchers utilized data from over 1,000 participants involved in the Parkinson’s Progression Markers Initiative (PPMI), a key study initiated by The Michael J. Fox Foundation to speed up research and treatment discovery.

They analyzed brain tissues from 24 deceased individuals, ten of whom had Parkinson’s at the time of death, while 14 did not. The virus was found in half of those with Parkinson’s, but in none of the control brains.

HPgV is a widespread, asymptomatic infection previously thought not to invade the brain. Current estimates suggest that about 4% of Americans have an ongoing HPgV infection, with up to 12% having encountered the virus at some stage in their lives.

The primary transmission method is through contact with infected blood, such as through shared needles or, historically, through blood transfusions prior to widespread screening.

Patients with a specific gene mutation linked to Parkinson’s, known as LRRK2, showed a more pronounced immune response to the virus compared to those without the mutation.

This genetic mutation altered the brain’s immune pathways when the virus was present in the bloodstream, triggering a harmful inflammatory response that wouldn’t occur in isolation.

The resulting inflammation led to further brain damage associated with Parkinson’s, particularly affecting neurons in the substantia nigra area, a key aspect of the disease.

Dr. Koralnik expressed surprise at the high frequency of the virus in Parkinson’s patients compared to controls. The unexpected variation in immune responses based on genetic background added an intriguing dimension to the findings.

This possibility hints that environmental factors could interact with the body’s response in unexpected ways.

Moreover, the researchers also found the virus in the spinal fluid of Parkinson’s patients, yet none in individuals without the condition.

As Parkinson’s progresses, the dopamine-producing area of the brain deteriorates. Dopamine plays a crucial role not only in the reward system but also in controlling movement.

Insufficient dopamine levels can disrupt the brain’s movement circuitry, resulting in rigidity, tremors, and challenges with initiating actions like rising from a chair.

Patients harboring the virus in their brain tissue displayed higher levels of toxic tau protein and abnormal protein levels relating to advanced disease stages.

Tau generally aids in stabilizing brain cell structures. However, when it becomes misfolded or damaged, it signals that the brain cell is on the decline.

Finding elevated tau pathology suggests a connection between the virus and more extensive brain cell damage beyond the typical dopamine cell loss seen in pure Parkinson’s cases.

The results were shared in the journal JCI Insight.

Currently, treatment options for Parkinson’s are somewhat limited and largely focus on alleviating symptoms rather than slowing disease progression.

Levodopa (L-Dopa) is regarded as the primary and most effective treatment. The brain converts L-Dopa into dopamine, replacing the crucial chemical that leads to motor symptoms.

Estimations indicate that over 10 million people globally, including around one million Americans, have Parkinson’s disease, with projections suggesting this figure could rise to over 25 million by 2050.

Dr. Koralnik plans to further investigate how genes like LRRK2 influence immune responses to various viral infections, aiming to uncover whether this phenomenon is specific to HPgV or part of a broader viral interaction.

One pressing question remains how frequently the virus enters the brains of individuals with or without Parkinson’s. The aim is to unravel how viruses and genes interact, providing insights that might illuminate the origins of Parkinson’s and assist in developing future treatments.