Combined Alpha-synuclein Test May Aid Disease Diagnosis, Monitoring

Using both ELISA and SAA tests may yield more information about disease severity

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Researchers have developed a test that may help to more accurately diagnose Parkinson’s disease and monitor its progression. It combines two already-used laboratory techniques to measure clumps of alpha-synuclein in the cerebrospinal fluid (CSF).

Alpha-synuclein is the protein that progressively builds to toxic levels in the brain and spinal cord of Parkinson’s patients. CSF is the liquid that surrounds the brain and spinal cord. The test was found to accurately distinguish Parkinson’s patients from healthy people and measured alpha-synuclein levels to determine disease severity.

These findings suggest the new test may be used to not only diagnose Parkinson’s, but to also monitor its progression and response to treatments, the researchers noted.

The findings were detailed in the study “Disease-Associated α-Synuclein Aggregates as Biomarkers of Parkinson Disease Clinical Stage,” published in Neurology.

Parkinson’s disease is usually diagnosed after clinical symptoms emerge, “but the neurodegenerative process is thought to begin many years before overt clinical symptoms  are observed,” the researchers wrote.

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Disease biomarkers are thus needed to identify at-risk patients, monitor disease progression, and to distinguish Parkinson’s from other neurodegenerative conditions.

Since nerve cell loss in Parkinson’s disease is mainly triggered by the toxic buildup of misfolded alpha-synuclein clumps, the protein is an attractive target for diagnostic tests. A number of methods have been employed to detect its clumps in human tissues or fluids.

The enzyme-linked immunosorbent assay (ELISA) is a fast and sensitive antibody-based approach for measuring protein levels, and can detect the amount of these clumps, or oligomers. Therefore, it can potentially monitor changes in these levels over time and upon treatment.

However, its “diagnostic accuracy in distinguishing [Parkinson’s patients] from controls has been unsatisfactory,” the researchers wrote.

Meanwhile, the seed amplification assay (SAA) has been shown to be extremely sensitive at distinguishing Parkinson’s patients from healthy people and those with other diseases, potentially allowing for a definitive diagnosis.

SAAs assess a protein’s seeding activity, or the rate at which a protein clumps together to form toxic aggregates. This involves introducing a small amount of a lab-made alpha-synuclein protein to a biological sample.

In diseases where alpha-synuclein aggregates, this lab-made protein will be recruited and incorporated into clumps, which can then be amplified and detected.

However, current SAAs “are mainly binary tests (positive or negative) with only semi-quantitative readout, rendering them suboptimal for monitoring longitudinal changes in levels of [alpha-synuclein] aggregates over the course of a disease or in response to a treatment,” the researchers wrote.

Combined diagnostic test more accurate

An international team of researchers investigated whether a combination of ELISA and SAA could provide an accurate readout of CSF alpha-synuclein clumps that could reflect disease severity in patients.

This approach used SAA to sensitively identify the presence of misfolded alpha-synuclein clumps, which could then be accurately quantified by ELISA.

First, they explored the test’s potential in brain tissue from people with Parkinson’s, dementia with Lewy Bodies (DLB), Alzheimer’s disease, and from healthy people who served as controls. DLB and Alzheimer’s are both neurodegenerative diseases, but only DLB is marked by alpha-synuclein buildup.

The combined approach was extremely sensitive at distinguishing Parkinson’s and DLB patients from Alzheimer’s patients and healthy controls. It also allowed for the aggregates to be detected earlier than with SAA alone.

Next, the team evaluated the diagnostic effectiveness of the combined test using CSF samples from 62 Parkinson’s patients (58% women), with a mean age of 57.5, and 34 age-matched healthy people (47% women).

Results again showed the test could discriminate between people with and without Parkinson’s with high accuracy.

In addition, alpha-synuclein clump levels measured with the combined approach were significantly associated with Parkinson’s severity, as assessed with the validated Unified Parkinson’s Disease Rating Scale-Part-III and the Hoehn and Yahr scale. In contrast, when SAA was used alone, the results were not linked to measures of clinical severity.

The observed association between the combined test readout and disease severity was then confirmed in a second group of CSF samples — 49 Parkinson’s patients (mean age 64) and 48 age- and sex-matched healthy people.

Results were similar to those in the first group, again showing significant correlations between test output and both measures of Parkinson’s severity.

The findings overall support the combined ELISA-SAA test for detecting Parkinson’s disease and its severity.

“We have established and validated a novel approach to provide clinical information about underlying disease severity in patients with [Parkinson’s], and thus perhaps a promising tool to support clinical trials targeting [alpha-synuclein] aggregates in [Parkinson’s],” the researchers wrote, noting future studies that tested patients over time could reveal more about the approach’s potential.

Future research should also assess whether this combined approach is useful with other alpha-synuclein-associated diseases, and in testing therapies that target protein aggregation, they said.

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