in short:
● The APOE e4 gene increases the risk of developing Alzheimer's. A new study suggests that people with the gene are also more likely to develop a loss of smell around age 65.
● Changes in the sense of smell can be an early sign of neurodegenerative diseases such as Alzheimer's and other dementias.
● Experts say the development of a smell test could become part of routine tests to detect Alzheimer's.
A recent study by researchers at the University of Chicago found a possible link between a gene associated with Alzheimer's disease and the loss of the sense of smell around age 65. Based on the findings, the researchers think that the loss of the sense of smell around this age could be an early warning sign of neurodegenerative disease.
The study involved 865 people who were tested at five-year intervals. The tests tested their ability to identify odors and asked them what they smelled. DNA samples were also collected to see which participants carried the APOE e4 gene, a known risk factor for developing Alzheimer's disease.
The researchers found that those who carried the gene were 37% less likely to be successful at identifying smells around age 65 than people who did not carry the gene. By age 75, people with the gene also began to lose the ability to identify smells.
Study author Dr. Matthew GoodSmith, MD, notes that the findings “identified only a relative decline in odor detection ability in people who carry the APOE e4 gene.” However, Goodsmith said the team hopes the study “will spark greater interest in exploring the links between smell loss, cognitive decline, and dementia risk.”
Why does smell seem to be linked to the development of Alzheimer's?
Researchers already know that a decline in the ability to smell is linked to degenerative diseases, including Parkinson's and Alzheimer's. Often, the first signs of neuronal degeneration occur in the olfactory cortex, the part of the brain that controls the sense of smell.
Zara Patel, an otolaryngologist and olfactory disorders specialist at Stanford Health Care, notes that the current study is just the latest of many to show similar findings. “The first signs of brain degeneration are in the olfactory cortex, so of course, losing that sense would be the first sign.”
Our ability to smell begins in the mucous membranes of our nose. Electrical signals are sent via the olfactory nerve directly to the olfactory cortex in the brain (the olfactory cortex), which processes smell.
The olfactory nerve also sends signals to the parts of the brain responsible for emotions and memories (the amygdala and hippocampus, respectively). These connections may explain why certain smells evoke specific emotions and memories.
Research suggests that most people diagnosed with Alzheimer's have impaired olfactory function, but the reason for this is not fully understood. Scientists think that changes in certain nerve proteins and neurotransmitters in the parts of the brain that help us smell may play a role in the early stages of the disease.
Other degenerative diseases that can affect the sense of smell include:
– Parkinson's disease
– Huntington's disease
– Multiple sclerosis (MS)
– Mild cognitive impairment
– Side effects of stroke
Is smell part of the Alzheimer's diagnosis?
According to the Alzheimer's Association, there is no single test that can confirm that a person has dementia. Instead, doctors usually need to do a variety of imaging, tests, and scans to definitively diagnose Alzheimer's disease.
Current tests and screenings for early detection of Alzheimer's include:
– Medical history
– Physical examination (e.g., blood pressure check, medication review, lifestyle information)
– Blood and urine tests
– Neurological examination (e.g., reflexes, muscle strength, speech, eye movement)
– Brain scans (e.g., MRI, CT scan)
– Cerebrospinal fluid tests (e.g., spinal fluid)
Although loss of smell can be an early sign of neurodegeneration, it is not currently included in screening tests for Alzheimer's and other dementias. However, this could change. Researchers at the University of Warwick are working on a smell and taste test that could become part of routine health checks and early detection tests for Alzheimer's.
What else causes loss of smell?
Olfactory dysfunction can be caused by a variety of conditions. In recent years, the most prominent has been COVID-19. At times during the pandemic, loss of smell and taste has been one of the most common symptoms of the virus.
There are a wide range of conditions that can cause loss of the sense of smell, ranging from fairly harmless conditions to more serious ones:
– Older age
– Trauma or injury
– Allergies
– Cold or flu
– Congestion
– Sinusitis
– Nasal polyps
– Metabolic disorders
– Post-viral disorders
– Tumors
Should you see a doctor if you experience loss of sense of smell?
You don't necessarily need to panic if you notice changes in your sense of smell, but it's something to pay attention to.
For example, if you thought your loss of smell was due to a recent cold, but you're feeling better but your sense of smell hasn't returned or things don't smell "normal," don't ignore it.
It may turn out to be something simple that will get better on its own. If not, you may need to see a doctor who specializes in smell. If you're older, know that you have the gene that puts you at higher risk for Alzheimer's, and if you're losing your sense of smell, your GP may want you to see a neurologist for further testing.
● The APOE e4 gene increases the risk of developing Alzheimer's. A new study suggests that people with the gene are also more likely to develop a loss of smell around age 65.
● Changes in the sense of smell can be an early sign of neurodegenerative diseases such as Alzheimer's and other dementias.
● Experts say the development of a smell test could become part of routine tests to detect Alzheimer's.
A recent study by researchers at the University of Chicago found a possible link between a gene associated with Alzheimer's disease and the loss of the sense of smell around age 65. Based on the findings, the researchers think that the loss of the sense of smell around this age could be an early warning sign of neurodegenerative disease.
The study involved 865 people who were tested at five-year intervals. The tests tested their ability to identify odors and asked them what they smelled. DNA samples were also collected to see which participants carried the APOE e4 gene, a known risk factor for developing Alzheimer's disease.
The researchers found that those who carried the gene were 37% less likely to be successful at identifying smells around age 65 than people who did not carry the gene. By age 75, people with the gene also began to lose the ability to identify smells.
Study author Dr. Matthew GoodSmith, MD, notes that the findings “identified only a relative decline in odor detection ability in people who carry the APOE e4 gene.” However, Goodsmith said the team hopes the study “will spark greater interest in exploring the links between smell loss, cognitive decline, and dementia risk.”
Why does smell seem to be linked to the development of Alzheimer's?
Researchers already know that a decline in the ability to smell is linked to degenerative diseases, including Parkinson's and Alzheimer's. Often, the first signs of neuronal degeneration occur in the olfactory cortex, the part of the brain that controls the sense of smell.
Zara Patel, an otolaryngologist and olfactory disorders specialist at Stanford Health Care, notes that the current study is just the latest of many to show similar findings. “The first signs of brain degeneration are in the olfactory cortex, so of course, losing that sense would be the first sign.”
Our ability to smell begins in the mucous membranes of our nose. Electrical signals are sent via the olfactory nerve directly to the olfactory cortex in the brain (the olfactory cortex), which processes smell.
The olfactory nerve also sends signals to the parts of the brain responsible for emotions and memories (the amygdala and hippocampus, respectively). These connections may explain why certain smells evoke specific emotions and memories.
Research suggests that most people diagnosed with Alzheimer's have impaired olfactory function, but the reason for this is not fully understood. Scientists think that changes in certain nerve proteins and neurotransmitters in the parts of the brain that help us smell may play a role in the early stages of the disease.
Other degenerative diseases that can affect the sense of smell include:
– Parkinson's disease
– Huntington's disease
– Multiple sclerosis (MS)
– Mild cognitive impairment
– Side effects of stroke
Is smell part of the Alzheimer's diagnosis?
According to the Alzheimer's Association, there is no single test that can confirm that a person has dementia. Instead, doctors usually need to do a variety of imaging, tests, and scans to definitively diagnose Alzheimer's disease.
Current tests and screenings for early detection of Alzheimer's include:
– Medical history
– Physical examination (e.g., blood pressure check, medication review, lifestyle information)
– Blood and urine tests
– Neurological examination (e.g., reflexes, muscle strength, speech, eye movement)
– Brain scans (e.g., MRI, CT scan)
– Cerebrospinal fluid tests (e.g., spinal fluid)
Although loss of smell can be an early sign of neurodegeneration, it is not currently included in screening tests for Alzheimer's and other dementias. However, this could change. Researchers at the University of Warwick are working on a smell and taste test that could become part of routine health checks and early detection tests for Alzheimer's.
What else causes loss of smell?
Olfactory dysfunction can be caused by a variety of conditions. In recent years, the most prominent has been COVID-19. At times during the pandemic, loss of smell and taste has been one of the most common symptoms of the virus.
There are a wide range of conditions that can cause loss of the sense of smell, ranging from fairly harmless conditions to more serious ones:
– Older age
– Trauma or injury
– Allergies
– Cold or flu
– Congestion
– Sinusitis
– Nasal polyps
– Metabolic disorders
– Post-viral disorders
– Tumors
Should you see a doctor if you experience loss of sense of smell?
You don't necessarily need to panic if you notice changes in your sense of smell, but it's something to pay attention to.
For example, if you thought your loss of smell was due to a recent cold, but you're feeling better but your sense of smell hasn't returned or things don't smell "normal," don't ignore it.
It may turn out to be something simple that will get better on its own. If not, you may need to see a doctor who specializes in smell. If you're older, know that you have the gene that puts you at higher risk for Alzheimer's, and if you're losing your sense of smell, your GP may want you to see a neurologist for further testing.
