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Loss of Smell: An Early Sign of Alzheimer's Disease?

Loss of Smell: An Early Sign of Alzheimer's Disease?

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A recent study discovers that people who are at high risk of developing Alzheimer’s disease could lose their sense of smell before cognitive decline.

Highlights:
  • Alzheimer’s disease is the most common form of dementia and diagnosis is usually a challenge
  • People who have a higher hereditary risk of Alzheimer's disease may lose their sense of smell before cognitive decline sets in
  • The study suggests that loss of smell could be a potential diagnostic tool for Alzheimer's disease
Identifying the early signs of Alzheimer's disease can be tricky. People who have a gene mutation that increases their chance of developing Alzheimer's disease may lose their sense of smell before they start to lose cognitive function, which might be a warning of a more serious form of the disease. The study was published in the journal Neurology.

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The Relationship Between Alzheimer’s Gene and Loss of Smell

APOE e4 is the gene variation linked to an increased risk of Alzheimer's.
"Testing a person's ability to detect odors may be a useful way to predict future problems with cognition," said study author Matthew S. GoodSmith, MD, of the University of Chicago.

"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."

The study comprised an at-home survey in which over 865 participants were tested on their sense of smell—both their capacity to perceive an odor at all and their ability to identify the odor they were perceiving. The tests were conducted every five years. People's cognitive and memory abilities were also assessed twice, five years apart. DNA samples revealed to researchers who contained the gene linked to an increased risk of Alzheimer's (1 Trusted Source
Association of APOE ε4 Status With Long-term Declines in Odor Sensitivity, Odor Identification, and Cognition in Older US Adults

Go to source
).

Scores for the odor detection test varied from zero to six based on how many distinct concentrations of scents participants could identify.

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APOE e4 Gene Could be the Reason Behind Weak Smell

At a particular time point, persons who carried the gene variation were 37% less likely to have strong odor recognition than people who did not carry the gene. Other characteristics that may influence the results, such as age, gender, and educational level, were taken into consideration by the researchers.

At the ages of 65 to 69, the gene carriers began to experience impaired scent perception. At that age, gene carriers could identify an average of 3.2 odors, compared to 3.9 smells for persons who did not have the gene.

People having the gene variation had no difference in their ability to recognize the odor they were perceiving until they were 75 to 79 years old. When individuals began to lose their capacity to distinguish scents, gene carriers deteriorated faster than those who did not contain the gene.

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Gene Variation Linked to Faster Cognitive Decline

At the outset of the investigation, the two groups' thinking and memory abilities were comparable. However, as predicted, individuals who had the gene variation suffered faster decreases in their cognitive skills over time than those who did not possess the gene.

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

The loss of smell could be a potential diagnostic tool for Alzheimer’s disease. A limitation of the study is that people with severe dementia were not included.

Reference:
  1. Association of APOE ε4 Status With Long-term Declines in Odor Sensitivity, Odor Identification, and Cognition in Older US Adults - (https://pubmed.ncbi.nlm.nih.gov/37495381/)


Source-Medindia


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