Tears May Contain a Biomarker for Parkinson's Disease

Thursday, February 22, 2018

A preliminary study will be presented at the American Academy of Neurology (AAN) meeting in Los Angeles, April 21-27, that shows there may be a biomarker in tears for Parkinson’s disease (PD).

Study author Mark Lew said, "We believe our research is the first to show that tears may be a reliable, inexpensive, and noninvasive biological marker of Parkinson's disease." The research team investigated proteins secreted by the lacrimal gland into the tear fluid as a potential measure of function for the nerves that innervate the lacrimal gland. Because PD affects these nerves as well as the central nervous system (CNS), Lew’s team hypothesized that changes in protein levels in tears could serve as a biomarker for PD.

Tear samples from 55 people with PD were analyzed for levels of four proteins and compared to protein levels in tear samples from 27 normal control subjects of the same age and gender. Researchers found differences in levels of alpha-synuclein and oligomeric alpha-synuclein, which is an aggregated form of alpha-synuclein that has been implicated in nerve damage in PD. Researchers noted it is also possible that the tear-gland secretory cells produce different forms of alpha-synuclein that can be directly secreted into tears.

The tears from patients with PD had decreased levels of alpha-synuclein (mean = 423 picograms per milligram (pg/mg) compared to tears from subjects without PD (mean = 704 pg/mg). However, levels of oligomeric alpha-synuclein were increased in tears from people with PD (mean = 1.45 ng/mg) compared to subjects without PD (mean = 0.27 ng/mg).

"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 noninvasive manner is exciting," said Lew. "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."

Further research in larger groups of patients and controls will help investigate when these changes begin to occur to determine whether differences in the levels of alpha-synuclein and oligomeric alpha-synuclein can be seen at the earliest stages of disease or before symptoms are first seen.

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