Sniffing out Alzheimer's early

Canadian researchers have found that a simple smell test may help in diagnosing those at risk of developing Alzheimer’s disease. And it is substantially cheaper (as well as far less invasive) than the lumbar puncture that is currently required for diagnosis of AD.

“Despite all the research in the area, no effective treatment has yet been found for AD ... But, if we can delay the onset of symptoms by just five years, we should be able to reduce the prevalence and severity of these symptoms by more than 50%”, said co-author Dr John Breitner from McGill University’s Centre for Studies on Prevention of Alzheimer’s Disease at the Douglas Mental Health Research Centre.

While the best known symptom of AD is memory loss, by the time this becomes obvious it is almost too late as the cognitive decline is well established. The idea of a smell test for cognitive decline in potential AD patients is credited to a University of Florida graduate student, Jennifer Stamps, whose simple peanut-butter-and-ruler test paved the way for the current research.

The McGill University team tested nearly 300 at-risk volunteers and then performed lumbar punctures on the 100 who had the most difficulty in identifying a range of odours, including bubblegum, gasoline and lemons. Among the 100 worst performers on the smell test the levels of various proteins associated with AD in their cerebrospinal fluid was conclusive.

“This is the first time that anyone has been able to show clearly that the loss of the ability to identify smells is correlated with biological markers indicating the advance of the disease,” said first author Marie-Elyse Lafaille-Magnan, a doctoral student at McGill University.

The authors cautioned that loss of olfactory abilities is not a conclusive test as there are other medical conditions which affect our sense of smell but it is a good (and simple) primary indicator.

“For more than 30 years, scientists have been exploring the connection between memory loss and the difficulty that patients may have in identifying different odours. This makes sense because it’s known that the olfactory bulb (involved with the sense of smell) and the entorhinal cortex (involved with memory and naming of odours) are among the first brain structures to be affected by the disease.”

Published in the journal Neurology, this study was supported by Pfizer Canada, the Canada Fund for Innovation, the Fonds de Récherche du Québec–Santé, the Levesque Foundation and The Douglas Mental Health University Institute Foundation.

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