a new study suggests. For the study, researchers used a chemical assay to detect clumping of the protein alpha-synuclein, a hallmark of Parkinson’s disease, in autopsy skin samples taken from patients who had Parkinson’s disease confirmed by brain pathology and from controls without the disease. The test showed a high degree of sensitivity and specificity for the diagnosis of Parkinson’s disease.
The study was published online in Movement Disorders.
“This test has a lot of promise,” said senior author, professor of biomedical sciences at Iowa State University in Ames. “At present there are no peripheral biomarkers for Parkinson’s disease. The current diagnosis is just based on symptoms, and the symptoms can be similar to many other neurological diseases,” he added. “It can take many years to establish a correct diagnosis and the accuracy is low even with experienced neurologists.”
If the current results can be replicated in samples from live patients and in those with very early stages of Parkinson’s disease, a skin test could allow early diagnosis and the possibility of starting preventive treatments to slow disease progression before symptoms develop too severely, the researchers suggest.
Sensitive and specific test
The blinded study used a seeding assay – used previously to detect misfolded proteins in prion diseases – to analyze 50 skin samples provided by the Arizona Study of Aging and Neurodegenerative Disorders/Brain and Body Donation Program based at Banner Sun Health Research Institute in Sun City.
Half of the skin samples came from patients with Parkinson’s disease and half came from people without neurologic disease. The protein assay correctly diagnosed 24 out of 25 patients with Parkinson’s disease and only one of the 25 controls had the protein clumping.
“At present, the only way to definitely diagnose Parkinson’s disease is on autopsy – by the detection of alpha-synuclein clumps [Lewy bodies] in the brain,” commented, professor of neurology at Mayo Clinic Arizona in Scottsdale and a coinvestigator of the study. “In our research, we have also seen clumping of alpha-synuclein in many other organs including submandibular gland, colon, skin, heart, and stomach, but in terms of access, the skin is probably the easiest source.”
In this study, “we found this seeding assay for alpha-synuclein clumps to be extremely sensitive and specific in the diagnosis of Parkinson’s disease,” he added. “This is very valuable data as we have samples from patients with autopsy-validated Parkinson’s disease.”
A reliable biomarker?
The researchers are now starting a study in living patients with funding from the National Institutes of Health in which they will repeat the process comparing skin samples from patients with clinically diagnosed Parkinson’s disease and controls.
“We need to know whether analyzing alpha-synuclein clumping in skin biopsies from live patients with Parkinson’s disease would serve as a reliable biomarker for disease progression. Will clumping of this protein in skin samples increase over time and does it correspond with disease progression?” Dr. Adler said.
In future they are also hoping to test individuals who have not yet developed Parkinson’s disease but may have some prodromal type symptoms and to test whether this assay could measure a treatment effect of drug therapy.
Dr. Adler noted that they are currently conducting an autopsy study of skin samples from individuals who did not have clinical Parkinson’s disease when alive but in whom Lewy bodies have been found postmortem.
“This suggests that the disease pathology starts before Parkinson’s symptoms develop, and in the future, if we can diagnose Parkinson’s disease earlier then we may be able to stop progression,” he said.
“There is a long list of compounds that have been studied to try and slow progression but haven’t shown benefits, but by the time patients develop symptoms they already have significant disease and [have] lost most of their dopamine neurons,” he added. “If we could backtrack by 10 years, then these drugs may well make a difference.”
Dr. Adler also noted that currently more advanced patients may undergo invasive procedures such as deep brain stimulation or surgery. “It is of utmost importance that they have an accurate diagnosis before being subjected to such procedures.”
In addition, he pointed out that an accurate test would help the drug development process. “It is vitally important to enroll patients with an accurate diagnosis in clinical trials of new drugs. At present, a large percentage of patients in these trials may not actually have Parkinson’s disease, which makes it very difficult to show a treatment effect.”