Scientists have developed a test for Parkinson’s disease based on its signature odour after teaming up with a woman who can smell the condition before tremors and other clinical symptoms appear.

The test could help doctors diagnose patients sooner and identify those in the earliest stages of the disease, who could benefit from experimental drugs that aim to protect brain cells from being killed off.

Perdita Barran, of the University of Manchester, said the test had the potential to decrease the time it took to distinguish people with normal brain ageing from those with the first signs of the disorder. “Being able to say categorically, and early on, that a person has Parkinson’s disease would be very useful,” she said.

Most people cannot detect the scent of Parkinson’s, but some who have a heightened sense of smell report a distinctive, musky odour on patients. One such “super smeller” is Joy Milne, a former nurse, who first noticed the smell on her husband, Les, 12 years before he was diagnosed.

Milne only realised she could sniff out Parkinson’s when she attended a patient support group with her husband and found everyone in the room smelled the same. She thought little more about it until she mentioned the odour to Tilo Kunath, a neurobiologist who studies Parkinson’s at Edinburgh University.

Kunath tested Milne’s skills by having her sniff T-shirts worn by either healthy people or Parkinson’s patients. Milne identified all those worn by the patients and said one more T-shirt bore the same scent. Eight months later, the wearer was diagnosed with the disease.

For the latest study, Barran worked with Kunath and Milne to identify the main substances that give rise to the distinctive Parkinson’s odour. They focused on compounds in sebum, a waxy fluid that is secreted by glands in the skin, particularly on the upper back where Milne said the scent was strongest.

The scientists used a technique called mass spectrometry to measure levels of volatile chemicals in sebum on swabs from Parkinson’s patients and healthy volunteers. By testing different groups, they whittled down the number of fragrant compounds from thousands to just four that appear to be most important for the scent.

Writing in the journal ACS Central Science, the researchers describe how Milne confirmed that mixtures of the four compounds had the same musky smell as Parkinson’s patients. Tests found that levels of three substances, eicosane, hippuric acid and octadecanal, were all higher than normal in the sebum of Parkinson’s patients, while levels of a fourth substance, perillic aldehyde, were lower.

To see whether the test can spot Parkinson’s before doctors can, the scientists have teamed up with researchers in Austria who study people with REM sleep disorders. A separate study found people with a specific kind of such disorder have a 50% risk of developing Parkinson’s in later life.

“If we can detect the disease early on, that would be very good news. It would mean we have a test that picks it up before motor symptoms appear,” Barran said.

In parallel, more than 1,000 Parkinson’s patients and hundreds of healthy people will have their sebum analysed to see how reliable the test is. Scientists will also look at whether changes in the odour reflect the progression of the disease, or even different forms of Parkinson’s.

Werner Poewe, the director of neurology at the Medical University of Innsbruck, said diagnosing Parkinson’s early and accurately was critical to giving patients the best advice and treatment. The discovery of a Parkinson’s scent “opens up an entirely new approach to test for the presence of Parkinson’s by a non-invasive test that only involves swabbing a piece of gauze across the neck region of a patient,” he said.

“Identifying [early] stages of the disease in those who have not yet developed classical signs and symptoms of Parkinson’s disease is a necessary first step to eventually testing new treatments that will delay or prevent the onset of this illness,” Poewe added.

Milne, whose sense of smell is so sensitive she has to avoid the more fragrant aisles of supermarkets, has identified the scents of other diseases too. To her, Alzheimer’s smells vaguely of vanilla, while cancer has a more earthy odour. In her next collaboration with the Manchester group, the aim will be to identify chemicals that produce a signature odour for tuberculosis.