Genetic Risk Of Dementia And Alzheimer’s Disease
Dementia is a term used to describe a group of symptoms associated with a drop in an individual’s cognitive abilities. While dementia can be caused by a wide array of medical conditions and environmental factors, certain risk genes, such as the APOE gene associated with late onset Alzheimer’s disease, can indicate a higher chance of developing Dementia.
Should I get genetically tested?
If you have reason to believe that you are more susceptible to developing dementia and/or Alzheimer’s disease or are concerned about developing Alzheimer’s as you age, genetic testing can either help you put your mind at ease, or help you prepare for the future.
One of the most researched risk gene with the greatest effect on Alzheimer’s risk is the APOE gene; every individual carries two copies of the APOE gene in their DNA that are inherited from their parents (one copy from each parent).
Research has shown that individuals who inherit two copies of the APOE4 variant of the APOE gene are eight to twelve times more at risk of developing Alzheimer’s disease than individuals without the APOE4 variant.
Please read the segment below on Alzheimer’s genes and genetic risk if you are interested in a more in depth look at the APOE gene and how it works.
While there is no known cure for dementia and Alzheimer’s disease, risk-factor reduction can help to potentially prevent or delay the development of both conditions. Additionally, due to the progressive nature of both conditions, early diagnosis and intervention is vital for managing the symptoms of early-stage dementia or Alzheimer’s disease.
Testing positive for risk genes does not mean you will get dementia or Alzheimer’s disease, but genetic testing can help to confirm the doctor’s diagnosis in the preclinical and mild cognitive impairment stages of Alzheimer’s development for patients who are already suspected to have Alzheimer’s disease, but are unable to get a proper diagnosis due to their symptoms being too mild to be diagnosed conclusively.
Early genetic screening is thus a useful tool for assessing the risk of developing dementia/ Alzheimer’s disease and helping the affected individual plan ahead to make the necessary lifestyle changes needed to reduce their risk factor.
Genetic testing at The Clifford Clinic
The Clifford Clinic is an aesthetic clinic that strives to be a hub for both aesthetics and medical health, in addition to offering comprehensive health screening and cancer screening services, Clifford Clinic also offers:
- Diagnostic genetic screening and testing services for checking for the presence of risk genes or causative genes associated with dementia/Alzheimer’s disease
- Deterministic tests to confirm the development of dementia/Alzheimer’s disease in patients already showing symptoms of either disease
What is genetic testing?
Genetic testing involves the examination of a person’s DNA to reveal possible mutations in the patient’s genetic code that may cause certain diseases. DNA and genes are only “visible” via genetic testing, and knowing what specific variation of certain genes a person carries can help explain health problems or confirm a medical diagnosis. Genetic testing is usually performed via a simple cheek swab or blood sample, and results of the test are usually ready within a few weeks.
Misconception about dementia
Dementia (senile dementia) is characterised as a gradual decline in an individual’s cognitive ability, impairing their capacity to perform everyday activities and tasks. A common misconception is that dementia is a disease; Dementia is not a disease, it is a collective term that describes a set of symptoms brought about by various medical conditions that impact an individual’s behaviour, memory, ability to think, and/or ability communicate.
Dementia vs Alzheimer’s disease – Alzheimer’s disease is a progressive brain disorder/disease, while “dementia” is a general term for a decline in mental ability that usually impact memory. A person can have dementia but not Alzheimer’s disease, but it is worth noting that Alzheimer’s disease is the leading cause of dementia.
Another common misconception is that dementia is a natural result of aging and can only occur in older individuals. Although age does increase the risk of dementia, dementia and its causes are not natural results of aging and are usually the result of neurodegenerative disorders or trauma to the brain. Additionally, while rare, young onset dementia affects individuals in their 30s to 50s and accounts for an estimated 10% or less of all dementia cases.
Symptoms of dementia
There are many different forms of dementia and the symptoms exhibited by each individual may vary depending on the cause of their dementia. However, individuals suffering from dementia generally display neuropsychiatric (neurological and psychological) symptoms such as:
- Memory loss
- Confusion and/or disorientation
- Difficulty communicating/ decline in linguistic ability
- Decline in spatial and visual abilities (For example, inability to navigate when driving or walking)
- Decline in cognitive ability related to problem solving, reasoning, and/or critical thinking
- Poor physical/motor coordination (poor muscle control)
- Abrupt personality change
- Increased paranoia and anxiety
Most of the symptoms listed above are usually noticed by someone other than the individual suffering from dementia themselves. If your loved one is suffering from memory loss or exhibit other symptoms of dementia, it would be advisable to consult a doctor to get a diagnosis.
Causes of dementia
Many of the causes of dementia can be classified as neurodegenerative disorders/diseases and a mix of variable factors such as age, medical history, lifestyle choices, and genetics can affect the likelihood of developing any one of these disorders. Some of the more common disorders/diseases that cause loss of or damage to the neurons (nerve cells) located in the brain include:
Alzheimer’s disease – the most common cause of dementia accounting for 60 to 80% of cases of dementia. Alzheimer’s disease causes brain shrinkage and the eventual atrophy (death) of brain cells, leading to dementia.
Cerebrovascular disease – causes vascular dementia by affecting the blood supply to the brain, and is the second most common type of dementia accounting for about 20% of dementia cases.
Synucleinopathies – neurodegenerative diseases characterised by abnormal accumulation of neuronal protein in neurons that results in Parkinson’s disease dementia or dementia with Lewy bodies (DLB)
Dementia can also result from physical damage to the brain; traumatic brain injury, or repetitive head injury, throughout the course of a person’s life can increase the risk of dementia. This form of dementia occurs predominantly in athletes who participate in “rough” spots like boxing or soldiers.
Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterised by the shrinking of the brain and eventual death of brain cells/neurons caused by abnormal accumulation of specific proteins in the brain. The most common symptom of early-stage AD is short-term memory loss, but as the disease progresses, disorientation, behavioural problems/mood swings, decline in linguistic ability, and eventually loss of bodily functions may be exhibited by the patient.
Late onset AD affects mainly individuals aged 65 years and above and is the most common cause of dementia. As mentioned above, dementia has many causes, the cause of dementia can usually be determined based on what first/early symptoms the patient exhibits; for example, hallucinations and attention problems indicate dementia with Lewy bodies. In the case of Alzheimer’s disease related dementia, the key first symptom is memory loss.
Stages of Alzheimer’s disease
Alzheimer’s disease is a slow progressing disease that is mild when it first develops but gradually worsens over several years. A person suffering from AD typically goes through five stages:
Preclinical stage – This is the starting stage before symptoms of AD become apparent. A patient can remain in the preclinical stage for years without any change in their behaviour that makes them, or the people around them, suspect that they have begun to develop AD.
Preclinical Alzheimer’s disease is diagnosed via the identification of amyloid plaques and neurofibrillary tangles in the brain via brain imaging scans or via the use of specific blood biomarkers. This stage of AD is thus usually only detected in clinical research settings as it is not likely for a doctor to order for a brain imaging scan or a blood test, with the specific AD biomarkers, to be done on an average patient for no reason.
Genetic tests can help you determine your genetic risk for early-onset Alzheimer’s disease to aid you and your doctor in deciding if it is worth considering getting regular blood work or brain scans done if your risk of AD is determined to be high. Early detection is vital for managing and delaying the progress of AD, and the preclinical stage is the earliest stage that AD can be detected.
Mild cognitive impairment (MCI) – Mild cognitive impairments such as minor memory lapses with regards to recent events or conversations, or slight difficulty when making decisions or carrying out tasks that require critical thinking. Symptoms are very mild but are generally noticeable.
It is important to note that due to how mild the symptoms are at this stage, MCI is often diagnosed based on the judgement of the patient’s doctor. Genetic testing, blood work, and/or brain imaging scans are useful for confirming the diagnosis at this stage as not all individuals with mild cognitive impairments have AD.
Mild dementia – Most patients are diagnosed with AD in this stage. Symptoms such as mild memory loss, impaired problem-solving skills, spatial disorientation, and decline in linguistic ability start to become apparent during this stage.
Moderate dementia – Symptoms listed in the moderate cognitive impairment stage start to worsen and the patient starts exhibiting other additional symptoms linked with dementia. The patient may undergo sudden and significant changes in their behaviour/personality and may need assistance with carrying out certain daily activities such as using the bathroom.
Severe dementia – Significant decline in cognatic function, during this late stage of AD, the patient’s physical capabilities and ability to move may also be impacted. Patients with severe dementia due to AD are typically unable to verbally communicate in a coherent manner, have difficulty carrying out motor tasks and require assistance with regards to personal care, and may exhibit abnormal reflexes due to muscle rigidity (eg. inability to walk or hold their heads up without support).
Alzheimer's genes and genetic risk
Alzheimer’s disease occurs due to an alteration in the brain’s protein clearance ability that leads accumulation of amyloid beta proteins in the brain, impacting normal neuronal functioning and connectivity.
Apolipoprotein E (Apo-E) is a fat-binding protein that is crucial for the breakdown and clearance of amyloid beta proteins to maintain normal brain function, thus, the presence of a particular variation in the genetic sequence of the APOE gene that codes for a “weaker” Apo-E is the strongest genetic risk factor associated with an increased risk of AD.
Apolipoprotein E4 (APOE) genotype
Apo-E is coded for by the APOE gene and variations in the sequence of the APOE gene (alleles) results in 3 common variations (isoforms) of Apo-E: E4, E3, E2.
Individuals with the Apo-E E4 genotype (APOE4) produce a variant of Apo-E that is not as effective at breaking down amyloid beta compared to the other variants, leading to abnormal buildup of amyloid beta in the brain. Testing positive for APOE4 thus indicates an increased risk of developing late onset AD. Conversely, individuals who carry the E2 variant are shown to have a reduced risk of Alzheimer’s as the E2 variant.
APOE4 is a risk gene – APOE alleles have the strongest association with Alzheimer’s disease, making it one of the strongest risk factors along with old age. In a study published in the Canadian Medical Association Journal, the APOE4 gene was shown to be most prevalent genetic risk factor, with more than half of all AD cases impacted by the APOE4 gene; around 40 to 80% of individuals with Alzheimer’s disease carry at least one allele of APOE4.
- Carrying one copy of the APOE4 gene increase the risk of developing Alzheimer’s disease by two to three times.
- Carrying two copies of the APOE4 gene increase the risk of developing Alzheimer’s disease by eight to twelve times.
The APOE4 gene was also shown to increase the risk for other form dementias; patients with the APOE4 gene are more likely to have increased severity of Lewy body dementia if they have Lewy bodies, and have an increased risk of developing Parkinson’s disease dementia.
Is it advisable to get genetically tested?
Circling back to the question “should I get genetically tested?”, due to the heritable nature of certain of the causes of dementia, genetic testing may be advisable if:
- Your family has a history of suffering from dementia and/or Alzheimer’s disease
- Someone in your immediate family tested positive for carrying a genetic risk factor
- You are experiencing symptoms of dementia/Alzheimer’s disease
As mentioned above, every individual carries two copies of the APOE gene in their DNA that are inherited from their parents; each parent contributing one copy of the gene. If one or both of your parents are/were diagnosed with Alzheimer’s disease or Alzheimer’s disease dementia, it might be advisable to get a genetic test done to determine if you have a higher risk of developing Alzheimer’s disease too.
Genetic testing is also recommended for individuals with no strong family history of dementia or Alzheimer’s disease but would like to know how high their risk of developing dementia is.
Genetic testing can be a useful tool that helps you make plans for the future, such as deciding beneficial lifestyle changes you may want to pursue, based on what genetic factors risk you are found to carry. It can also be useful for determining the chances of passing dementia/Alzheimer’s disease to your children should you and/or your partner be unfortunately found to be carrying causative genes of AD.
Please note that testing positive for risk genes associated with increased risk of dementia/Alzheimer’s disease does not predetermine that you will develop dementia or Alzheimer’s disease.
Our Certified Doctors
Dr. Gerard Ee
Dr. Gerard Ee is the founder and medical director of The Clifford Clinic. He is fully accredited in cosmetic treatments including fillers, Botox, light therapies, and more. Driven by his passion for sharing his expertise across the medical community, Dr. Ee has accumulated his surgical experiences internationally from working in the Mount Sinai Hospital in New York, National University Hospital (NUH), and Singapore General Hospital (SGH).
Dr. Chow Yuen Ho
Dr. Chow Yuen Ho is the founder and medical director of The Clifford Clinic. With over 10 years of clinical practice experience, the reputable aesthetic doctor specializes in non-invasive aesthetic and acne treatments. Dr. Chow has accomplished so much in this field. He served as the founding Director of Medical Informatics at SGH and then as the Managing Director of the Asian division of Alert Life Sciences Computing.
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