Smell of Parkinson’s

Biomedical Doctor Pablo Barrecheguren talks about the early diagnosis of Parkinson’s by the scent of the skin.

Of all our senses, perhaps one of the least valued today is the sense of smell. And yet, we all have strong emotional memories associated with some scent.

For example, we all remember our grandparents’ houses, which always had a characteristic smell. The Japanese call this scent kareishu, “the smell of the grandparents”, and science has discovered that its origin is that as the years go by we have higher levels of a molecule, 2-nonenal, in the skin.

This detail is interesting because it means that regardless of our level of hygiene, our smell changes according to our physical condition; and this leads to an interesting clinical question, can specific smells be associated with certain diseases?.

Several researchers are working on this topic, and among other things, it has been discovered that trained dogs are able to detect from a person’s breath whether they have colon cancer or not with 91% accuracy. This opens the door to the search for odorous molecules associated with certain diseases.

Joy Milne and her sense of smell for Parkinson’s disease

In this regard, one of the most researched fields is Parkinson’s, and it’s all thanks to one woman: Joy Milne. She had a husband who suffered from the disease and, when attending some talks in Edinburgh, she asked the speaker if people with Parkinson’s had a characteristic smell.

This anecdote led to two discoveries: the first is that, like great sommeliers, Joy had an extraordinary sense of smell, well above the average level. And the second is that Joy was capable, by simply smelling a person, of recognizing whether they had the scent that her husband had developed and, therefore, knowing whether they had Parkinson’s or not.

To verify it a pilot experiment was conducted where she smelled twelve t-shirts (six from healthy people and six from people with the disease); and her sense of smell was such that she got eleven out of twelve cases right, apparently being wrong when saying that one of the healthy people had Parkinson’s.

But time later this person was diagnosed with Parkinson’s, so Joy had been right in all twelve cases, even anticipating the clinical diagnosis and in fact she stated that her husband began to have that characteristic scent about six years before he was diagnosed with Parkinson’s.

After this first study, Joy continued collaborating with the researchers. Little by little they discovered that the origin of the smell had to be in the sebum, the fat, of the skin, which is interesting because dermatological problems have already been documented in patients with Parkinson’s.

And currently research is focusing on isolating the molecules responsible for this almost imperceptible smell: although work is still ongoing, some of the metabolites whose levels are altered in the patients’ dermal sebum are the perillaldehyde and the icosane, whose smell was described by Joy as very similar to the one her husband developed with Parkinson’s.

Besides being very curious, these investigations have great potential: currently Parkinson’s is only diagnosed once symptoms appear, and these are usually detected when approximately the 60% of the neurodegeneration causing the disease has already occurred.

That is to say, we diagnose the disease very late; therefore treatments arrive late and it is difficult to halt the neurodegeneration in time.

Even so, with current treatments the symptoms can be contained for much of the average 15 years that a patient lives with the disease, but we would surely be in a better situation if we could diagnose the disease earlier.

Conclusion

If it is confirmed that patients have different levels of certain molecules in the skin even before having Parkinsonian symptoms, then although we generally cannot personally detect the smell (almost no one has Joy’s sense of smell), it would be possible to take a sample of this bit of skin sebum, analyze it and see whether this person suffers from the disease or not.

Therefore, although it is still under study, it is possible that something as subtle as the scent could have a great impact on Parkinson’s research.

Bibliography

• Abellán, A. “Did you know that at thirty you begin to smell old?”. Principia Magazine.
• Morgan, J. (2016). Joy of super smeller: sebum clues for PD diagnostics. The Lancet Neurology, 15(2), 138–139.
• Sonoda, H., Kohnoe, S., Yamazato, T., Satoh, Y., Morizono, G., Shikata, K., … Maehara, Y. (2011). Colorectal cancer screening with odour material by canine scent detection. Gut, 60(6), 814–819.
• “‘Super-smeller’ helps develop swab test for Parkinson’s disease”. The Guardian.
• Trivedi, D. K., Sinclair, E., Xu, Y., Sarkar, D., Walton-Doyle, C., Liscio, C., … Barran, P. (2019). Discovery of Volatile Biomarkers of Parkinson’s Disease from Sebum. ACS Central Science.

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