An analysis of the protein content in tears may offer a non-invasive and inexpensive way of identifying people with probable Parkinson’s disease.
A study led researchers at the Keck School of Medicine of the University of Southern California reports that Parkinson’s patients have different levels of alpha-synuclein protein in tear fluid than do people who do not have the disease.
This finding suggests that tears may represent a reliable biomarker of Parkinson’s, one that might enhance early diagnosis of this progressive disorder.
The study, “Tear proteins as possible biomarkers for Parkinson’s disease,” was recently presented at the 2018 World Congress on Parkinson’s Disease and Related Disorders (IAPRD) in Lyon, France.
Parkinson’s disease is mostly recognized by selective loss of nerve cells in the brain that produce an important regulatory protein called dopamine. This is believed to be in part mediated by the accumulation of abnormal toxic protein clumps, mainly composed alpha-synuclein protein.
But disease effects are not restricted to the brain, and patients also experience progressive peripheral nerve cell damage.
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As the secretory cells of the tear gland are stimulated by nerves, researchers hypothesized that nerve alterations observed in Parkinson’s disease could result in altered protein content in tears.
A research team led by Mark Lew, MD, collected and evaluated tear samples from 94 Parkinson’s patients and 60 healthy volunteers matched for age and sex.
The researchers found that total levels of normal, non-clumped, alpha-synuclein were about 35% lower in patients’ tear fluid compared to healthy controls. In contrast, patients had an amount of alpha-synuclein toxic aggregates that was four times higher than controls (3.43 nanograms per milligram of tear proteins compared to 0.84 nanograms). The team had reported similar results previously in a smaller group of patients.
Now, the researchers also evaluated the levels of other potentially relevant proteins, including chemokine ligand 2 (CCL-2 ) and DJ-1 (Park 7), but failed to find any changes between the two groups.
Supported by these results, the researchers believe that evaluation of “total alpha-synuclein and oligomeric [aggregated] synuclein may have potential to discriminate between tears of Parkinson’s disease patients and healthy controls.”
“To our knowledge this is the first report of tear collection and protein analysis as a possible non-invasive, inexpensive, and reliable biomarker for Parkinson’s,” they added.