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APOE ε4 Affects Odor Sensitivity and May Help Predict Cognitive Decline
Assessing odor sensitivity could provide an early indicator of impending cognitive impairment. A recent study published in the journal Neurology has shed light on the association between the APOE ε4 allele and the decline of olfactory sensitivity, odor identification, and cognitive function in older adults. This allele has been known to increase susceptibility to Alzheimer disease (AD).
Using data from the National Social Life Health and Aging Project (NSHAP), a comprehensive survey of home-dwelling older adults in the United States, researchers from the University of Chicago, Illinois, aimed to explore “whether APOE ε4 is associated with decline of odor sensitivity and whether such decline serves as a harbinger of cognitive decline and AD.”
Researchers measured odor sensitivity in 865 respondents and odor identification in 1156 respondents, collected at multiple time points between 2005 and 2015. Cognitive function in 864 respondents was also assessed in 2010 and 2015 using a modified version of the Montreal Cognitive Assessment. Genotyping was conducted in 2010 to identify APOE ε4 carriers and noncarriers.
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The results of the study revealed that deficits in odor sensitivity were noticeable in APOE ε4 carriers between the ages of 65 and 69. However, odor identification deficits did not manifest until ages 75 to 79. Odor sensitivity did not decline more rapidly in APOE ε4 carriers as they aged (carrier status and aging interaction: odds ratio [OR] 1.44, 95% CI 0.94-2.19, p = 0.092), whereas odor identification showed a faster decline in carriers (aging 10 years interaction: OR 0.26, 95% CI 0.13-0.52, p < 0.001).
“As expected, and in parallel to odor identification, cognition declined more rapidly in APOE ε4 carriers (interaction: OR 0.55, 95% CI 0.34-0.89, p = 0.015),” researchers found.
This study highlights that APOE ε4 affects olfactory sensitivity earlier than odor identification or cognitive function. Further research aimed at “identifying the mechanism underlying these relationships will elucidate the key role of olfaction in neurodegeneration during aging,” researchers concluded.
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