A woman who could "smell Parkinson's" has helped scientists come up with a test which spots the disease.
The test has been years in the making after academics realised Joy Milne could smell the illness.
The 72-year-old from Perth, Scotland, has a rare condition which gives her a heightened sense of smell.
She noticed her late husband Les developed a different odour when he was 33 - some 12 years before he was diagnosed with the disease - which leads to parts of the brain become progressively damaged over many years.
Mrs Milne, dubbed 'the woman who can smell Parkinson's' described a "musky" aroma, different from his normal smell.
Her observation piqued the interest of scientists, who decided to research what she could smell, and whether this could be harnessed to help identify people with the neurological condition.
Years later, academics at the University of Manchester have made a breakthrough by developing a test which can identify people with Parkinson's disease using a simple cotton bud run along the back of the neck.
Possible NHS rollout
Researchers can examine the sample to identify molecules linked to the disease to help diagnose whether someone has the disease.
While still in the early phases of research, scientists are excited about the prospect of the NHS being able to deploy a simple test for the disease.
There is currently no definitive test for Parkinson's disease, with diagnosis based on a patient's symptoms and medical history.
If the new skin swab is successful outside laboratory conditions, it could be rolled out to achieve faster diagnosis.
Mrs Milne said it was "not acceptable" people with Parkinson's had such high degrees of neurological damage at the time of diagnosis.
"I think it has to be detected far earlier - the same as cancer and diabetes," she said. "Earlier diagnosis means far more efficient treatment and a better lifestyle for people."
She added: "It has been found that exercise and change of diet can make a phenomenal difference."
She said her husband, a former doctor, was "determined" to find the right researcher to examine the link between odour and Parkinson's, and they sought out Dr Tilo Kunath at the University of Edinburgh in 2012.
Dr Kunath paired up with Professor Perdita Barran to examine Mrs Milne's sense of smell.
The scientists believed the scent may be caused by a chemical change in skin oil, known as sebum, that is triggered by the disease.
In their preliminary work, they asked Mrs Milne to smell t-shirts worn by people who have Parkinson's and those who did not.
Mrs Milne correctly identified the t-shirts worn by Parkinson's patients, but she also said one from the group of people without Parkinson's smelled like the disease - eight months later the individual who wore the t-shirt was diagnosed with Parkinson's.
Researchers hoped the finding could lead to a test being developed to detect Parkinson's, working under the assumption if they were able to identify a unique chemical signature in the skin linked to Parkinson's, they may eventually be able to diagnose the condition from simple skin swabs.
In 2019 researchers at the University of Manchester, led by Prof Barran, announced they had identified molecules linked to the disease found in skin swabs.
And now the scientists have developed a test using this information.
Right treatment more quickly
The tests have been successfully conducted in research labs, and assessments are being made as to whether they can be used in hospital settings.
If successful, the test could potentially be used in the NHS so GPs can refer patients for Parkinson's tests.
The findings, which have been published in the Journal of the American Chemical Society, detail how sebum can be analysed with mass spectrometry - a method which weighs molecules - to identify the disease.
Some molecules are present only in people who have Parkinson's disease.
Researchers compared swabs from 79 people with Parkinson's with a heathy control group of 71 people.
The degenerative disease is the fastest growing neurological condition in the world. It has a variety of symptoms including tremors - particularly in the hands - gait and balance problems, slowness and extreme stiffness in the arms and legs.
Prof Barran said there was currently no cure for it, but a confirmatory diagnostic would allow patients to get the right treatment and drugs more quickly.
She said exercise and nutritional changes would also be advised, but "most critically, it will allow them to have a confirmed diagnosis to actually know what's wrong with them".
She added: "At the moment in Greater Manchester there are about 18,000 people waiting for a neurological consult and just to clear that list, without any new people joining it, will take up to two years.
"Of those, 10-15% are suspect Parkinson's. Our test would be able to tell them whether they did or whether they didn't (have Parkinson's) and allow them to be referred to the right specialist.
"So at the moment, we're talking about being able to refer people in a timely manner to the right specialism, and that will be transformative."
Can she smell other diseases?
Mrs Milne is now working with scientists around the world to see if she can smell other diseases like cancer and tuberculosis (TB).
"I have to go shopping very early or very late because of people's perfumes, I can't go into the chemical aisle in the supermarket, so yes, a curse sometimes but I have also been out to Tanzania and have done research on TB and research on cancer in the US - just preliminary work.
"So it is a curse and a benefit."
She said she can sometimes smell people who have Parkinson's while in the supermarket or walking down the street, but has been told by medical ethicists she cannot tell them.
"Which GP would accept a man or a woman walking in, saying 'the woman who smells Parkinson's has told me I have it'? Maybe in the future, but not now."