Early Loss of Smell May Signify Alzheimer’s Risk in APOE e4 Gene Carriers

Carriers of a particular genetic variant linked to an increased likelihood of Alzheimer’s disease, known as APOE e4, may experience an early loss of odor detection abilities.

This could potentially serve as an early indicator of future cognitive impairments, according to a study recently published in the American Academy of Neurology’s medical journal, Neurology®.

Matthew S. GoodSmith, MD, from the University of Chicago, and one of the study’s authors, suggests, “Testing a person’s ability to detect odors may be a useful way to predict future problems with cognition. While more research is needed to confirm these findings and determine what level of smell loss would predict future risk, these results could be promising, especially in studies aiming to identify people at risk for dementia early in the disease.”

Can Loss of Smell Indicate Alzheimer’s?

To find out, the study employed an at-home survey to test the olfactory abilities of over 865 participants, both their odor detection and identification skills.

The survey was conducted at five-year intervals, with participants’ cognitive and memory abilities also evaluated twice, five years apart.

DNA samples collected during the survey revealed which participants carried the Alzheimer’s associated genetic variant.

To measure people’s ability to detect odors, a scoring system ranging from zero to six was used, dependent on their capacity to perceive various odor concentrations.

Genetic Variant APOE e4 Effects

The study found that carriers of the APOE e4 variant were 37% less likely to exhibit proficient odor detection compared to those without the variant at a single timepoint.

This difference was observed even after considering other influential factors such as age, sex, and education level.

The decrease in smell detection for gene carriers began to manifest between the ages of 65 and 69, with an average detection rate of roughly 3.2 odors compared to the 3.9 odors detected by non-carriers.

The APOE e4 gene carriers did not exhibit a difference in their ability to identify specific odors until between the ages of 75 and 79. Once they began losing this ability, their decline was more rapid than those not carrying the variant.

While initial cognitive and memory abilities were similar across both groups, those carrying the gene variant experienced more rapid deterioration in cognitive abilities over time.

“Identifying the mechanisms underlying these relationships will help us understand the role of smell in neurodegeneration,” adds GoodSmith.

The study did have some limitations, including the absence of individuals with severe dementia.

It was supported by the National Institutes of Health, National Institute on Aging, and the National Institute of Diabetes and Digestive and Kidney Diseases.”

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