Science

Woman with exceptional sense of smell who can smell Parkinson’s disease helps develop diagnostic test

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Joy Milne, a 72-year-old Scottish woman living in Perth, has an unusual ability: her sense of smell allows her to detect Parkinson’s disease in humans. In particular, she noticed that her own husband, now deceased, had changed his body odor twelve years before he was diagnosed. His extraordinary talent enabled scientists to develop a new screening test.

Joy Milne actually suffers from a rare condition that causes her to have an oversensitive sense of smell (we’re talking about hyperosmia). Therefore, she easily noticed a change in her husband’s body odor, which became more “musky”, according to The Guardian. Twelve years later, the latter learned that he had Parkinson’s disease, a slowly progressive neurodegenerative disease characterized by the destruction of dopamine neurons and the accumulation of toxic protein clusters.

This woman apparently made headlines, and scientists decided to use this ability to develop a new test to detect this neurological disease. After years of research and development, researchers at the University of Manchester now come up with a practical and quick test: the latter involves running a swab along the back of the neck to collect any odorous molecules that indicate disease.

Changes in the chemical composition of sebum

How can Parkinson’s disease affect a person’s sense of smell? Increased oiliness and flaking of the skin, especially on the face and scalp, are common symptoms of this condition. The researchers then hypothesized that the disease causes a chemical modification of sebum, a lipid film secreted by the skin’s sebaceous glands, whose production is increased in those affected.

In people with Parkinson’s disease, the chemical composition of sebum is different, which gives them a specific smell. © D. Sarkar et al.

To test this hypothesis, they asked Joy Milne to sniff T-shirts, some of which were worn by people with the condition. She not only managed to identify all the T-shirts of sick people, but she also “smelled” the disease on the T-shirt of a healthy person … who was diagnosed eight months later!

This experiment showed that the disease is associated with a unique skin chemical signature that researchers could potentially use to make a diagnosis based on simple skin smears. In 2019, they succeeded in identifying the volatile compounds in question, specifically perylaldehyde and eicosan, whose levels change significantly when the disease occurs, leading to the test device being currently evaluated in the lab.

It is based on paper spray ionization combined with ion mobility mass spectrometry (PS-IM-MS). The researchers simply take a sample of sebum with a swab and then insert it into the device. Their method was applied to samples taken from 150 people (79 patients and 71 healthy controls).

Molecular composition of sebum in Parkinson's disease

Comparison of the molecular composition of the sebum of sick people (A, C) and healthy people (B, D). © D. Sarkar et al.

The analysis takes only three minutes – significantly faster than current clinical mass spectrometry methods. Another advantage of the method is that it allows the measurement of both low molecular weight and high molecular weight compounds that can be lost during sample preparation in more traditional analytical methods. In addition, specific compounds were found that are unique to sebum samples from Parkinson’s patients compared to healthy individuals. In particular, the researchers identified two classes of lipids, triacylglycerides and diglycerides, that are “significantly differently expressed” in disease.

“Non-invasive sampling followed by PS-IM-MS analysis targeting these compounds could provide an inexpensive test to support clinical phenotyping to confirm a diagnosis of Parkinson’s disease,” the team concludes.

On the way to rapid and early diagnosis of the disease

To date, the diagnosis of Parkinson’s disease is mainly based on the patient’s symptoms and medical history. But the disease is silent for a long time and it takes several years before the first symptoms appear. By this point, almost 50-70% of dopamine neurons have already been destroyed. The main motor symptoms due to the destruction of these neurons are akinesia (slow onset of movement), muscle rigidity, and tremor.

Diagnosis is difficult because these symptoms do not appear at the same time and are not of the same magnitude. Moreover, none of them is either disease-specific or systemic. In addition, no biological assay or imaging study to date has been able to establish the diagnosis with certainty. Result: in the majority of patients, severe neurological disorders are detected at the time of diagnosis. The new test discussed here could allow early treatment and offer patients a better quality of life.

“There are currently around 18,000 people in Greater Manchester waiting for a neurological consultation and it will take up to two years to clear that list without adding more people. Among these people, 10 to 15% suspect Parkinson’s disease,” complains Perdita Barra, who led the study. Parkinson’s disease is the fastest growing neurological disease in the world, with more than 20 million people expected to be affected by it by 2050.

This skin test is currently only in the prototyping phase, but if it proves effective outside of a laboratory setting, it could be quickly implemented to speed up diagnosis. It has been shown that in parallel with drug treatment, which consists of taking dopamine to relieve motor symptoms, exercise and an appropriate diet can help slow the progression of the disease. Hence the importance of early diagnosis. Meanwhile, Ms Milne is working with scientists around the world to see if she can smell other diseases like cancer and tuberculosis.

D. Sarkar et al., Journal of the American Chemical Society.

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