Those most at risk of developing Alzheimer’s may lose this sense before cognitive decline sets in, new research suggests

Those who carry a gene variant associated with the strongest risk of Alzheimer’s disease may lose their ability to detect smells before they begin to lose cognitive function—a potential sign of more severe disease to come.

That’s according to a new study published Wednesday in the journal Neurology, by researchers at the University of Chicago.

Researchers followed more than 1,000 older U.S. adults for 10 years, testing their genes, as well as their ability to smell and think at various intervals. Those who carry the APOE e4 gene variant—which has the strongest known association with developing the disease—began to struggle to detect smells between ages 65-69, a decade before those without the mutation. Both cognition and the ability to identify odors later declined more rapidly in carriers than non-carriers.

Those with the variant were nearly 40% less likely to have good odor detection at any given point in the study than those without the variant.

Given the results, “testing odor sensitivity may be useful to predict future impaired cognitive function,” the authors wrote.

The study used data collected from the National Social Life Health and Aging 

Project, which did not track whether participants eventually developed Alzheimer’s, Dr. Matthew GoodSmith, an internist at the University of Chicago and lead author on the study, told Fortune.

Still, the results “definitely suggest testing sense of smell as a potential diagnostic tool, or maybe as part of a battery of tools used to assess someone’s risk of developing full-blown Alzheimer’s disease,” he said.

“It gives us a little bit of information about the interplay between smell and loss of cognition, and we hope it will spur further research into this.”

Signs of Alzheimer’s disease

Alzheimer’s disease, a neurodegenerative condition, is the most common type of dementia. It begins with mild memory loss and may eventually progress to the inability to carry a conversation or respond to the environment, according to the U.S. Centers for Disease Control and Prevention.

Those who are concerned they or a loved one might have Alzheimer’s or another form of dementia should talk to their doctor, who may recommend they see another specialist, like a neuropsychologist or a neurologist.

Warning signs of the condition, according to the AARP, include:

  • Difficulty performing daily tasks like keeping track of bills and following a recipe while cooking
  • Repetition, such as asking the same question over and over and telling the same story multiple times
  • Struggling to find the right word
  • Getting lost
  • Personality changes, such as becoming more anxious, confused, afraid, or paranoid
  • Confusion about time and place, especially if someone can’t remember where they are or how they got there
  • Misplacing items in unusual areas
  • Trouble with hygiene
  • Trouble with handling money
  • Sudden loss of things one is usually interested in, including family, friends, work, and social events
  • Forgetting old memories

GoodSmith might add changes in sense of smell to the list. While there are many reasons someone might lose their sense of smell, the symptom “might increase a primary care doctor’s index of suspicion” and lead them to investigate Alzheimer’s in a patient with other potential signs, he said.

There’s currently no cure for Alzheimer’s, though treatment can alter the progression of the disease. Ever an optimist, GoodSmith said he feels as if “it’s only a matter of time before there are interventions to slow cognitive decline.”

If and when there are, being able to detect the condition as early as possible will be key—perhaps through a simple, noninvasive test like that of the sense of smell, he said.

“It might be a useful thing once we develop more active therapeutics.”

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