Tears may be used to diagnose Parkinson’s disease, according to preliminary findings of a study that will be presented at the 2018 American Academy of Neurology’s (AAN) Annual Meeting in Los Angeles, California, April 21-27.
“We believe our research is the first to show that tears may be a reliable, inexpensive and noninvasive biological marker of Parkinson’s,” Mark Lew, MD, the study’s author from the Keck School of Medicine of University of Southern California, said in a press release.
Parkinson’s disease is mainly characterized by selective loss of neurons that produce dopamine in a brain area called substantia nigra. Patients with Parkinson’s typically exhibit Lewy bodies – protein clumps mainly composed of aggregated alpha-synuclein – in the brain, leading to nerve damage and disease progression.
Besides pathological changes in the brain, the disease also affects nerve function in the periphery. As the secretory cells of the tear gland are stimulated by nerves, researchers hypothesized that nerve changes in Parkinson’s could result in altered protein levels in tears.
The scientists collected tear samples from 55 Parkinson’s patients and 27 healthy controls who were the same age and gender.
The tears were analyzed for the levels of four proteins. The results revealed that levels of normal, non-clumped alpha-synuclein were lower in Parkinson’s patients than in controls. However, levels of unhealthy, aggregated alpha-synuclein were increased in tears of Parkinson’s patients (1.45 nanograms per milligram of tear proteins versus 0.27 nanograms, respectively).
Researchers hypothesize that the secretory cells in the tear gland could themselves produce these different forms of alpha-synuclein, which would be secreted directly into tears.
“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,” Lew said.
“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,” he added.
Nonetheless, larger studies need to be done to evaluate whether these changes in alpha-synuclein levels can be detected in tears from Parkinson’s patients before symptoms start.