Alzheimer’s disease: Loss of smell as an early warning sign

Smell tests could help identify people at risk for Alzheimer's.

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Alzheimer’s disease is a neurodegenerative disorder characterized by progressive cognitive decline, memory loss, and impaired cognitive function. It is the most common cause of dementia in older adults. While the exact causes of Alzheimer’s are not fully understood, research has suggested a significant genetic component in its development.

Recent studies have indicated that individuals with an increased genetic risk of Alzheimer’s may exhibit specific early symptoms before the onset of cognitive decline. One such notable symptom is the loss of the sense of smell, known as anosmia. This study aims to investigate the potential link between elevated genetic risk of Alzheimer’s and the early occurrence of anosmia.

A study published in Neurology® on July 26, 2023 at American Academy of Neurology, reveals that individuals with the APOE e4 gene variant, linked to the highest risk of Smell tests could help identify people at risk for Alzheimer’s disease Dr. Matthew S. GoodSmith from the University of Chicago led the research, suggesting that this premature loss of smell could potentially predict future cognitive issues.

The study involved over 865 participants, with their sense of smell and cognitive abilities assessed at five-year intervals. DNA samples were collected to identify carriers of the APOE e4 gene variant. The findings imply that evaluating odor detection ability could be a valuable approach to predicting cognitive problems in the future, offering hope for identifying individuals at risk of dementia during the early stages of the disease. However, further research is required for confirmation.

In the study, individuals carrying the APOE e4 gene variant, associated with a higher risk of Alzheimer’s disease, had a 37% lower likelihood of good odor detection than non-carriers at a single time.. This reduction in smell detection started around ages 65 to 69, with carriers able to detect an average of about 3.2 different smells. In contrast, non-carriers could detect around 3.9 odors.

The ability to identify specific odors was the same between the ages 75 to 79 groups. From that point, the gene carriers experienced a faster decline in their odor identification ability than non-carriers. While both groups had similar thinking and memory skills at the beginning of the study, those carrying the gene variant exhibited a more rapid decline in their cognitive abilities over time compared to those without the gene.

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

In conclusion, this study highlights the significance of the sense of smell as an early marker for Alzheimer’s disease, particularly in individuals with an increased genetic risk. Anosmia may represent an accessible and cost-effective tool for identifying at-risk individuals at an earlier stage, opening up new possibilities for early intervention and personalized care. Future research should focus on understanding the underlying biological connections and developing targeted therapeutic approaches based on olfactory assessments for individuals at risk of developing Alzheimer’s disease.

Journal reference:

  1. Matthew S. GoodSmith, Kristen E. Wroblewski et al., Association of APOE ε4 Status With Long-term Declines in Odor Sensitivity, Odor Identification, and Cognition in Older US Adults. Neurology. DOI:10.1212/WNL.0000000000207659.
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