Testing the sense of smell of people at a high risk of Alzheimer's disease might help to provide an early diagnosis, a new study suggests.

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Loss of smell shows a positive correlation with Alzheimer's development, a new study suggests.

Alzheimer's disease is an irreversible condition characterized by memory loss and damage of other cognitive functions. At present, there are no effective ways of diagnosing progression toward Alzheimer's early on in populations that are at risk.

Diagnoses usually follow from the identification of mild cognitive impairment, but this may not be early enough for treatments to be significantly effective.

Currently, Alzheimer's disease is diagnosed following questions related to the individual's medical history and any recent behavioral and personality changes, memory and cognition tests, standard medical tests, or brain scans.

Researchers from the Centre for Studies on Prevention of Alzheimer's Disease at the Douglas Mental Health Research Centre of McGill University in Montreal, Canada, have started looking at ways of diagnosing Alzheimer's much earlier in a person's life.

First study author Marie-Elyse Lafaille-Magnan, a doctoral student at McGill University, alongside a team of researchers from this institution, are interested in seeing whether or not they can reliably diagnose Alzheimer's disease based on people's loss of their sense of smell.

Dr. John Breitner, the director of the Centre for Studies on Prevention of Alzheimer's Disease, hopes that early detection can result in effective action to prevent some of the symptoms of the disease. "[I]f we can delay the onset of symptoms by just 5 years, we should be able to reduce the prevalence and severity of these symptoms by more than 50 percent."

The researchers' findings were published in the journal Neurology and are available online.

'Loss of smell correlates with Alzheimer's'

The study was conducted on 274 participants considered to be at high risk of Alzheimer's disease because they had a parent who had been diagnosed with the condition. The average age of the participants was 64 years.

A multiple choice scratch-and-sniff test (the University of Pennsylvania Smell Identification Test) was conducted to ensure whether, and to what extent, each participant was able to identify a varied range of scents.

Additionally, 100 participants also offered to undergo lumbar punctures measuring the levels of Alzheimer's-related proteins in the cerebrospinal fluid, which is a "buffer" liquid found in the spinal cord and the brain.

All of the participants also went through traditional assessments, such as a review of the individuals' medical history and neurologic and cognitive examinations.

It was found that people for whom it was most difficult to identify different odors also exhibited other markers of Alzheimer's disease, as revealed by the additional assessments.

"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," says Lafaille-Magnan.

A correlation between the loss of the olfactory sense and the onset of Alzheimer's is not entirely surprising, according to the researchers, as the brain regions connected with memory and the sense of smell are affected by the disease in its early stages.

"This [correlation] 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 odors) are among the first brain structures to be affected by the disease."

Marie-Elyse Lafaille-Magnan

Smell tests may provide cheaper alternative

Dr. Breitner suggests that assessing the sense of smell of people at high risk of Alzheimer's disease might, at some point in the future, become a cheaper, less invasive alternative to some of the traditional examinations. He warns, however, that there is still a long way to go until that goal will be achievable.

"[A] simple smell test may potentially be able to give us information about the progression of the disease that is similar to the much more invasive and expensive tests of the cerebrospinal fluid that are currently being used," says Dr. Breitner.

For the time being, specialists advise that the same tests be carried out to diagnose Alzheimer's disease, since assessments of the sense of smell are still in their early stages.

Olfactory difficulties, Dr. Breitner cautions, might be indicative of other conditions, so all possibilities should be taken into account, without yet jumping to any conclusions. "[P]roblems identifying smells may be indicative of other medical conditions apart from [Alzheimer's disease] and so should not be substituted for the current tests," he concludes.