Tears could accurately diagnose Parkinson’s disease

Testing the tears of elderly people who might have Parkinson’s disease could be the most effective way of diagnosing the condition. According to a new study by the Keck School of Medicine of the University of Southern California in Los Angeles, biomarkers in the fluid could be key.

The scientists discovered tiny differences in the levels of a particular protein found in tears between those with the neurological condition and patients without it. By using this non-invasive method, many people could be treated prior to the onset of symptoms, resulting in a better response to drugs.

Parkinson’s affects one in 500 people, equating to 127,000 Brits, and currently has no cure. It can severely impair a patient’s independence, as movement becomes difficult and muscles stiffen up. Another common symptom is involuntary shaking, which makes many everyday tasks difficult to complete.

In the study, tear samples were taken from 55 Parkinson’s patients, as well as 27 people without the disease. The test subjects were of comparable age and gender, meaning a full analysis of the differences could be carried out.

Dr Mark Lew, a professor of neurology who was involved in the study, explained that the secretory cells of the tear gland contain various proteins. When the nerves are stimulated and tears produced, these proteins transfer into the fluid.

As Parkinson’s affects how the nerves outside of the brain function, researchers hypothesised that protein levels in tears could therefore change as a result of the condition. This led them to test out the theory, which found differences in the amount of alpha-synuclein protein between sufferers and control subjects.

Dr Lew said: “We believe our research is the first to show that tears may be a reliable, inexpensive and non-invasive biological marker of Parkinson's disease.”

Adding more detail to the analysis, the scientists discovered that oligomeric alpha-synuclein – a specific form of the protein – could be detected in tears. This is found in Parkinson’s patients, as it means the protein has formed aggregates, resulting in tissue damage.

What was discovered in the research was that those with Parkinson’s had a decreased total level of alpha-synuclein in their tears. It worked out at an average of 423 picograms per milligram compared to 704 picograms per milligram in the subjects without the condition.

The oligomeric alpha-synuclein protein levels were much higher in Parkinson’s sufferers, however. They stood at an average of 1.46 nanograms per milligram of tear protein in contrast to 0.27 nanograms per milligram in non-sufferers. The nanogram unit is 1,000 times bigger than a picogram.
Dr Lew concluded: “Knowing that something as simple as tears could help neurologists differentiate between people who have Parkinson's disease and those who don't in a non-invasive manner is exciting.

“And because the Parkinson's disease process can begin years or decades before symptoms appear, a biological marker like this could be useful in diagnosing, or even treating, the disease earlier.”

More studies into the potential of this breakthrough are planned, but it could lead to better management of the condition in future.