Losing your sense of smell? It could be Alzheimer’s

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Losing the olfactory sense, known as anosmia, is one of the first symptoms of the disease, say scientists. It predicts changes in brain regions important in dementia – opening the door to a cheap and non-invasive screening programme.

They would be as routine as going to the optician’s – to check out your vision or hearing. Clinical trials are now being planned.

Senior author Professor Jayant Pinto, of the University of Chicago in the US, said: “This study provides another clue to how a rapid decline in the sense of smell is a really good indicator of what’s going to end up structurally occurring in specific regions of the brain.”

Early diagnosis is vital. Drugs trials have failed so far because they are prescribed too late – once the memory-robbing condition has taken hold.

Memory plays a critical role in our ability to recognise odours. Scientists have long known of a link between sense of smell and dementia.

Alzheimer’s is believed to be triggered by plaques and tangles of rogue proteins that gather in neurons that control olfaction and memory – then spread to others.

The team analysed data on 515 older people from their US city who had been taking part in a memory and ageing project since 1997.

They demonstrated it was possible to identify alterations in the brain that correlated with an individual’s loss of smell and cognitive function over time.

Lead author Rachel Pacyna, a rising star in her fourth-year as a medical student, said: “

Our idea was people with a rapidly declining sense of smell over time would be in worse shape – and more likely to have brain problems and even Alzheimer’s itself – than people who were slowly declining or maintaining a normal sense of smell.”

Participants are tested annually for cognitive function, signs of dementia – and their ability to identify certain smells. Some have also received an MRI brain scan.

A rapid decline in olfactory skills during a period of normal cognition predicted multiple features of Alzheimer’s disease.

They included less grey matter in areas related to smell and memory, worse cognition and higher risk of dementia.

In fact, the risk of sense of smell loss was similar to carrying the APOE-e4 mutation – a known genetic risk factor for Alzheimer’s.

The changes were most noticeable in primary olfactory regions called the amygdala and entorhinal cortex.

They are linked to the hippocampus – the memory control centre and a critical site in Alzheimer’s.

Prof Pinto said: “We were able to show the volume and shape of grey matter in olfactory and memory-associated areas of the brains of people with rapid decline in their sense of smell were smaller compared to people who had less severe olfactory decline.”

An autopsy is the gold standard for confirming Alzheimer’s. He hopes to eventually extend the findings by examining patient brain tissue.

Smell tests in clinics are also being planned – in ways similar to how vision and hearing tests are used.

Older adults would be screened and tracked for early-doors dementia. It could lead to the development of new treatments.

Smell tests are an inexpensive and easy-to-use. The tool described in Alzheimer’s & Dementia consists of a series of sticks that are similar in appearance to felt-tip pens.

Each is infused with a distinct scent that individuals must identify from a set of four choices.

Ms Pacyna said: “If we could identify people in their 40s, 50s and 60s who are at higher risk early on, we could potentially have enough information to enroll them into clinical trials and develop better medications.”

Bigger studies taking more MRI (magnetic resonance imaging) brain scans may help pinpoint when structural changes in the brains begin – or how quickly they shrink.

Prof Pinto added: “We have to take our study in the context of all of the risk factors that we know about Alzheimer’s, including the effects of diet and exercise.

“Sense of smell and change in the sense of smell should be one important component in the context of an array of factors that we believe affect the brain in health and ageing.”

He has previously examined sense of smell as an important marker for declining health in older adults. It’s often overlooked – compared to our ability to ssee and hear.

In 2014 a paper revealed older adults with no sense of smell were three times more likely to die within five years.

It was a better predictor of death than a diagnosis of lung disease, heart failure or cancer.

The number of dementia cases worldwide will triple to over 150 million by 2050. New treatments are desperately needed – and early diagnosis is key.

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