Alzheimer’s disease is not completely genetic or hereditary. In very rare cases, a specific gene can directly lead to Alzheimer’s. In more common cases, having a first-degree family member with Alzheimer’s increases your risk but does not guarantee you will develop Alzheimer’s.
Being older than 65 is the most common non-genetic risk factor for developing Alzheimer’s disease.
Simply put, having a family history of dementia makes it more likely that you will experience dementia. However, people with no family history still develop Alzheimer’s and people with a robust family history of dementia may not get it.
Alzheimer’s disease is a neurodegenerative disease and the most common form of dementia, which results in memory impairment and general cognitive decline. About 6 million people have Alzheimer’s disease in the United States alone, including those who developed it at a younger age.
It is caused by the buildup of beta-amyloid plaque (caused by amyloid peptides) and tau tangles in the brain, destroying brain cells (neurons). These buildups may be influenced by many factors:
C2N Diagnostics released a simple blood test (PrecivityAD) in 2020 that can measure levels of amyloid plaque particles in your blood plasma, as well as determine if an individual possesses the APOE gene that increases your risk of developing Alzheimer’s.
This test marks the first time healthcare providers can take a regular blood sample and predict the presence of Alzheimer’s with up to 86% accuracy. It’s safe to say, more genetic testing will soon enter the market to compete.
Let’s dive into everything you need to know about the genetics behind Alzheimer’s disease.
How Genetics Impact Your Risk of Alzheimer’s
There are certain genes/mutations that increase your risk of Alzheimer’s, and a few very rare genes/mutations that may directly cause Alzheimer’s disease.
These extremely rare genes that directly cause Alzheimer’s are called “deterministic genes”. Those that only increase your chances of developing Alzheimer’s are called “risk genes”.
Experts do not recommend routine genetic testing to diagnose Alzheimer’s. There may be very rare genes that may directly cause early-onset Alzheimer’s, but genetic testing cannot give you a 100% accurate diagnosis or prediction.
The most common gene associated with higher disease risk is the APOE-e4 allele. Interestingly, individuals with APOE-e2 variation have a decreased risk for the development of Alzheimer’s.
Does Alzheimer’s run in the family? Alzheimer’s runs in the family, in a sense. Those who have a first-degree relative (parent or sibling) with the disease are at increased risk of developing Alzheimer’s. This does not equate to a 100% guarantee that you’ll develop the disease. But genetics seem to partially contribute to developing Alzheimer’s.
Can you get Alzheimer’s if it doesn’t run in your family? You can get Alzheimer’s if it doesn’t run in your family. The causes of Alzheimer’s disease are not purely genetic. Age is the biggest risk factor for developing the disease. Everyone older than 65 years old is at risk of developing Alzheimer’s. However, having no family history of dementia may decrease your risk of dementia.
Does Alzheimer’s skip a generation? According to the research available, having a parent with Alzheimer’s increases your risk, but having a grandparent with Alzheimer’s does not necessarily increase your risk.
Is Alzheimer’s passed on by mother or father? Alzheimer’s is not passed on by the mother more than the father, or vice versa. A mother or father may pass on an “Alzheimer’s gene” or mutation that increases your risk. Even if both your parents pass on a risk gene, your Alzheimer’s risk is higher, but not certain.
What are the chances of getting Alzheimer’s if a parent has it? The chances of getting Alzheimer’s if a parent has it are higher than someone with no family history of dementia (not certain, but higher).
If a parent develops early-onset Alzheimer’s disease, their child has a high risk of developing the early-onset form as well. If both parents pass on genes that lead to early-onset dementia, that child has a very strong probability of developing early-onset familial Alzheimer’s disease (FAD), also called autosomal dominant Alzheimer’s.
Alzheimer’s and Down Syndrome
Down syndrome may give researchers hints at how the 21st chromosome affects the development of Alzheimer’s disease.
In Down syndrome, an individual has an extra copy of chromosome 21. This 43rd chromosome overall leads to symptoms, such as a flattened facial appearance, slant eyes, short neck, small ears, small hands and feet, and intellectual and/or developmental problems.
Moreover, individuals with Down syndrome develop Alzheimer’s at a much higher rate than the rest of the population, and at a much younger age.
Which genes are responsible for Alzheimer’s?
APOE-e4 is the most common gene associated with Alzheimer’s, but it is only a risk gene. It doesn’t necessarily guarantee you’ll develop the disease.
Alzheimer’s disease genetics can seem complicated. That might be because researchers don’t know every gene on every chromosome that may lead to Alzheimer’s. But scientists have figured out 3 deterministic genes that result in Alzheimer’s disease, as well as several genes and genetic mutations that bring a greater risk of Alzheimer’s.
Deterministic genes are only found in an estimated 1% of Alzheimer’s cases. Here are the 3 deterministic genes that directly cause Alzheimer’s, particularly early-onset Alzheimer’s disease:
- Presenilin 1 (PSEN1)
- Presenilin 2 (PSEN2)
- Amyloid precursor protein (APP)
Mutations or variations of the following genes may put you at higher risk of Alzheimer’s, especially late-onset Alzheimer’s disease:
- SORL1 (some variations on chromosome 11)
Apolipoprotein E-e4 (APOE4) was identified in 1993 as the first gene variation (not a gene mutation) found to increase the risk of Alzheimer’s disease. According to the Alzheimer’s Association, “researchers estimate that between 40-65% of people diagnosed with Alzheimer’s have the APOE-e4 gene.”
There is a blood test that tests for APOE-e4. This genetic test helps inform an Alzheimer’s diagnosis, though it cannot diagnose Alzheimer’s by itself.
At-Home Genetic Tests for Alzheimer’s Genes
No at-home test can effectively diagnose Alzheimer’s disease. However, there is an at-home genetic test that helps your doctor know whether to look into more effective Alzheimer’s diagnostic tools.
The 23andMe Personal Genome Service Genetic Health Risk (GHR) test can identify genes associated with 10 diseases, including late-onset Alzheimer’s. You send a saliva sample through the mail, then get back genetic data that helps you understand your risk.
Areas of Future Research
According to the National Institute on Aging, here are some questions to answer in future research into the association between Alzheimer’s and genetics:
- How genetics interact with lifestyle factors to affect Alzheimer’s risk
- How the disease process begins
- Why Alzheimer’s is the most common cause of dementia symptoms (but not the only one)
- What the difference in Alzheimer’s between various racial groups and sexes
- How to prevent Alzheimer’s
- What treatments are possible and effective
- Who is most at risk for Alzheimer’s, and why
How to Reduce Your Risk of Developing Alzheimer’s
It is difficult to say with certainty how to reduce your risk of developing Alzheimer’s disease and the memory loss it causes. But many researchers have shown certain lifestyle changes can slow or even prevent Alzheimer’s.
In fact, there is increasing evidence that chronic inflammation due to lifestyle factors, not amyloid plaque buildup, is the true underlying cause of Alzheimer’s disease.
Experts suggest the following lifestyle changes can reduce your risk of developing Alzheimer’s disease:
- Eat healthy (limit sugar and processed foods, eat plenty of fiber and healthy fats, etc.)
- Exercise regularly
- Regulate high blood pressure
- Keep cholesterol low
- Quit smoking
- Avoid excess alcohol
- Address gingivitis
- Control diabetes, heart disease, and other systemic illnesses
Because most — if not all — conventional dementia treatments have about a 1% chance of success, the need for a revolutionary new approach is critical for improving brain health and treating dementia and Alzheimer’s.
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- Castro, P., Zaman, S., & Holland, A. (2017). Alzheimer’s disease in people with Down’s syndrome: the prospects for and the challenges of developing preventative treatments. Journal of neurology, 264(4), 804-813. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5374178/
- Schupf, N. (2002). Genetic and host factors for dementia in Down’s syndrome. The British Journal of Psychiatry, 180(5), 405-410. Full text: https://www.cambridge.org/core/services/aop-cambridge-core/content/view/B12DD2DC2DA2191ADCC4780D09B32B14/S0007125000160787a.pdf/genetic_and_host_factors_for_dementia_in_downs_syndrome.pdf
- Williamson, J., Goldman, J., & Marder, K. S. (2009). Genetic aspects of Alzheimer disease. The neurologist, 15(2), 80. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3052768/
- Gustafson, C. (2015). Dale E. Bredesen, MD: Reversing Cognitive Decline. Integrative Medicine: A Clinician’s Journal, 14(5), 26. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4712873/