Scientists are edging closer to diagnosing Parkinson's disease via a "game-changing" skin swab.
The tremor-causing condition occurs when nerve cells become lost in a part of the brain that produces the chemical messenger dopamine, which helps control and co-ordinate body movements.
Existing diagnostic guidelines have no set test, with a medic assessing a suspected patient's symptoms, medical history and physical capabilities.
Scientists from the University of Manchester have found, however, people with Parkinson's have changes to the oily substance sebum, which coats and protects the skin.
After looking at 500 people with and without the disease, the team discovered 10 chemical compounds that are elevated or reduced in the sebum of Parkinson's patients.
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This enabled the scientists to distinguish between those with and without the condition with 85% accuracy.
Around 145,000 people are diagnosed with Parkinson's in the UK, with one in 37 expected to be told they have the disease in their lifetime.
"We believe our results are an extremely encouraging step towards tests that could be used to help diagnose and monitor Parkinson's," said co-lead author Professor Perdita Barran.
"Not only is the test quick, simple and painless but it should also be extremely cost-effective because it uses existing technology that is already widely available.
"We are now looking to take our findings forwards to refine the test to improve accuracy even further and to take steps towards making this a test that can be used in the NHS, and to develop more precise diagnostics and better treatment for this debilitating condition."
The research initially received funding after it came to light "super smeller" Joy Milne could distinguish between people with and without Parkinson's based on their odour, before any symptoms had emerged.
Milne, whose husband was diagnosed with Parkinson's aged 45, is thought to pick up on the scent of their sebum. Parkinson's patients have been found to produce more sebum than normal in some cases.
To learn more, the Manchester scientists collected sebum samples from the upper back of 500 people with and without the disease.
Mass spectrometry, an analytical tool that measures molecules, revealed subtle but fundamental changes to a patient's sebum as their Parkinson's progressed, they published in the journal Nature Communications.
These changes specifically affected the patients' cells' fat-processing and their mitochondria, energy powerhouses.
A skin swab may therefore be able to diagnose the disease and monitor its' development, enabling medics to gauge whether a new treatment is helping to slow or reverse Parkinson's, according to the Manchester scientists.
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Parkinson's vague and slow-developing symptoms, like muscle stiffness and slow movement, mean it is often confused for other neurological conditions.
While there is no cure, treatments can ease symptoms and improve a patient's quality of life, with these therapies often being most effective when prescribed early in the disease's onset.
A recent survey of more than 2,000 patients by Parkinson's UK found just over a quarter (26%) reported initially being misdiagnosed.
Of these, almost half (48%) were treated based on their misdiagnosis, with just over a third (34%) claiming the unnecessary therapy made their health worsen.
One who knows the reality of this all too well is Daxa Kalayci, 56.
"I was misdiagnosed with anxiety, stress-related tremors and told my problems stemmed from going through the menopause," she said.
"I embarked on a four-month cruise across the globe not knowing I had Parkinson's.
"Just two weeks into the trip, my symptoms worsened and my dream holiday turned into a nightmare."
Kalayci, from Leicester, endured "unpleasant side effects" from drugs prescribed for other suspected conditions.
She was eventually diagnosed with Parkinson's via a DaTscan, a device many specialists use to confirm the loss of dopamine-producing cells. The NHS does not recommend this appliance specifically, but says brain scans may be used to rule out conditions other than Parkinson's.
"I lost so many years not being able to pursue a career as a paramedic or go back to nursing," said Kalayci.
"This test could be a game-changer for people living with Parkinson's and searching for answers like I was.
"The sooner this test is available, the better. Anything that can help people looking for a diagnosis is a bonus."
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Professor David Dexter from Parkinson's UK, added: "We are proud to have part-funded this groundbreaking research which marks a significant step towards developing a quick and accurate test that can not only revolutionise the way we diagnose Parkinson's, but also allow us to monitor how this debilitating condition progresses.
"Every hour, two more people in the UK are diagnosed with Parkinson's and a significant portion of these people may well have been misdiagnosed with, and treated for, another condition before receiving their correct diagnosis.
"This has been compounded in the COVID-19 [the disease caused by the coronavirus] pandemic where people have been left waiting and have faced months of anxiety to confirm their diagnosis by a health professional.
"With this innovative test, we could see people being diagnosed quickly and accurately, enabling them to access vital treatment and support to manage their Parkinson's symptoms sooner."
The Manchester scientists have filed patents for their diagnostic techniques and are planning to create a spin-out company to commercialise new tests. They are also actively seeking investors to help drive their project.