New smell test could aid early detection of Alzheimer's and Parkinson's

October 11, 2017
smell
Credit: Petr Kratochvil/public domain

Nisha Pradhan was seven when she began to suspect she was missing out on something. Her sister seemed to have an uncanny knack for predicting what their mother was making for dinner. Pradhan, meanwhile, never had a clue.

"I would just stare at her," Pradhan says. "She's younger than me—how does she know more than I do?"

Now 21, Pradhan knows she has a limited ability to detect odor—including the smell of dinner cooking. Her situation is not unique: The sense of smell is often taken for granted, until it malfunctions.

As a patient in a clinical trial being conducted at Rockefeller University, Pradhan is helping scientists develop new smell tests, which promise to help improve diagnosis because they can be used reliably for anyone, anywhere. Because smell disorders can be linked to a variety of health conditions—interfering with appetite, as well as social interaction and sometimes leading to isolation, anxiety, and depression.

"People have their vision and hearing tested throughout their lives, but smell testing is exceedingly rare," says neuroscientist Leslie Vosshall.

The new tests, developed by Vosshall along with Julien Hsieh, a Rockefeller clinical scholar, and their colleagues could even aid the early detection of neurological disorders that have been linked to problems with olfaction.

An underappreciated skill

People suffer from for various reasons—a head trauma or sinus infection, for example, or even a common cold—and the cause can be as hard to pinpoint as the condition itself. In Pradhan's case, she believes she lost much of her sense of smell as a young child, although she's not sure how. She brought the issue up with her pediatrician, but never received any testing or guidance.

Both the medical community and the people affected by smell loss can be prone to overlook it. "Olfies," says Pradhan, referring to people with a normal sense of smell, "think not having a sense of smell just affects our ability to detect gas leaks, smoke, and bad body odor. But it deprives us of so much more, including emotions and memories that are so intimate and integral to the human experience."

A handful of tests already exist for diagnosing people like her. One problem with these tests is that they rely on a patient's ability to detect and identify single types of odor molecules, such as rose-scented phenylethyl alcohol. However, the ability to detect odors and to recognize them can vary greatly between people. So, someone with an otherwise normal sense of smell may not be able to detect the rose molecule. Meanwhile, another person who can smell roses but is from an area where these flowers are scarce may struggle to put a name to the scent. In either case, there is the potential for misdiagnosis, particularly when testing across different populations and countries.

The problem of smell

Hsieh and colleagues set out to eliminate these potential biases with the help of "white smells," made by mixing many odors together to produce something unfamiliar. Just as a combination of wavelengths of light produces white light, and many frequencies of sound make up white noise, the team generated white smells from assortments of 30 different . Their two new tests ask patients to distinguish white smells with overlapping ingredients and to detect white smells at increasingly lower concentrations.

If a person is unable to detect a single component of the scent, this has little effect on the outcome, and test takers don't need to identify the at all. "We're really excited about these new tests," says Vosshall, who is Robin Chemers Neustein Professor and a Howard Hughes Medical Institute investigator. "They focus on the problem of smell itself, because they don't force people to match smells to words."

Clinical trials conducted at The Rockefeller University Hospital and Taichung Veterans General Hospital in Taiwan showed that the new tests detected smell loss more reliably than conventional options. The results, published in Proceedings of the National Academy of Sciences, open up the possibility of a new means to detect smell loss worldwide. It could be used for detection of Alzheimer's and Parkinson's diseases, says Hsieh, now a resident at the Geneva University Hospitals in Switzerland.

"The goal is to use changes in the sense of , along with other biomarkers, to identify underlying causes of these neurological disorders very early, and so potentially improve treatment," he says.

Explore further: Early odor exposure enhances response of smell cells

More information: Julien W. Hsieh et al, SMELL-S and SMELL-R: Olfactory tests not influenced by odor-specific insensitivity or prior olfactory experience, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1711415114

Related Stories

Early odor exposure enhances response of smell cells

September 25, 2017
Mice exposed to scents of mint or fresh cut grass before and shortly after birth show increased responses in a specific population of odor-processing neurons to a variety of odors, according to new research published in eNeuro. ...

Elderly who have trouble identifying odors face risk of dementia

September 29, 2017
A long-term study of nearly 3,000 adults, aged 57 to 85, found that those who could not identify at least four out of five common odors were more than twice as likely as those with a normal sense of smell to develop dementia ...

For some, smell test may signal Parkinson's disease up to 10 years before diagnosis

September 6, 2017
A simple scratch-and-sniff test may one day be able to help identify some people at greater risk of developing Parkinson's disease up to 10 years before the disease could be diagnosed, according to a new study published in ...

Could olfactory loss point to Alzheimer's disease?

August 16, 2017
By the time you start losing your memory, it's almost too late. That's because the damage to your brain associated with Alzheimer's disease (AD) may already have been going on for as long as twenty years. Which is why there ...

Loss of smell linked to increased risk of early death

March 22, 2017
In a study of adults aged 40 to 90 years who were followed for 10 years, poor smell was linked with an increased risk of dying.

Recommended for you

'Selfish brain' wins out when competing with muscle power, study finds

October 20, 2017
Human brains are expensive - metabolically speaking. It takes lot of energy to run our sophisticated grey matter, and that comes at an evolutionary cost.

Researchers find shifting relationship between flexibility, modularity in the brain

October 19, 2017
A new study by Rice University researchers takes a step toward what they see as key to the advance of neuroscience: a better understanding of the relationship between the brain's flexibility and its modularity.

Want to control your dreams? Here's how

October 19, 2017
New research at the University of Adelaide has found that a specific combination of techniques will increase people's chances of having lucid dreams, in which the dreamer is aware they're dreaming while it's still happening ...

Brain training can improve our understanding of speech in noisy places

October 19, 2017
For many people with hearing challenges, trying to follow a conversation in a crowded restaurant or other noisy venue is a major struggle, even with hearing aids. Now researchers reporting in Current Biology on October 19th ...

Investigating the most common genetic contributor to Parkinson's disease

October 19, 2017
LRRK2 gene mutations are the most common genetic cause of Parkinson's disease (PD), but the normal physiological role of this gene in the brain remains unclear. In a paper published in Neuron, Brigham and Women's Hospital ...

New procedure enables cultivation of human brain sections in the petri dish

October 19, 2017
Researchers at the University of Tübingen have become the first to keep human brain tissue alive outside the body for several weeks. The researchers, headed by Dr. Niklas Schwarz, Dr. Henner Koch and Dr. Thomas Wuttke at ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.