Genetic Risk and Alzheimer’s Disease: Should You Worry?
Dr. Elisabeth Sherman
Alzheimer’s Disease is now so common that almost all of us have experienced a family member slowly succumb to the condition. Could this also happen to you?
Alzheimer’s Disease or Normal Aging?
Alzheimer’s Disease is the most common of all dementia. It is a devastating, slowly progressive brain disease characterized by severe memory loss. There was a time when becoming “senile” was seen as just another part of the aging process. Now we know better. Alzheimer’s, like diabetes or heart disease, are all chronic and yet common conditions that have both genetic (inherited) and non-genetic causes.
Is there a Genetic Risk in Alzheimer’s Disease?
The baseline risk of getting Alzheimer’s Disease is 10 to 15%. Around 15-30% of people with Alzheimer’s have a first-degree relative with the disease (a parent or sibling). About 75% of cases have no family history of Alzheimer’s Disease at all. And only about 5% of all Alzheimer’s cases are due to an autosomal-dominant gene.
The vast majority of people with Alzheimer’s Disease have what is called late-onset Alzheimer’s Disease. The late-onset form affects 95% of people with the disease, and is by far the most common form of dementia. There is no known single gene attributed to late-onset Alzheimer’s Disease.
Researchers have identified susceptibility genes that confer the relative likelihood, or risk, but not certainty, for the late-onset disease. The main susceptibility gene is the apolipoprotein E gene (APOE), which is involved in lipid transport and cholesterol function. One of the three forms of this gene (the APOE ε4 allele) is associated with a 50 – 55% increase in the lifetime risk of Alzheimer’s Disease, and only if you have two copies of the ε4 allele.
Some people without the APOE ε4 gene develop Alzheimer’s Disease, and some people with it never develop the disease at all.
Should I consider Genetic testing for the disease?
Risk of susceptibility to the disease increases with age, with the highest likelihood found in those over 85. Late-onset Alzheimer’s Disease is difficult to predict, as your risk is influenced not only by genetics, but also lifestyle and environmental factors. For this reason, genetic testing is not recommended for the late-onset form, but is best considered in early-onset disease, where genetics play a larger role.
Young-onset or early-onset Alzheimer’s Disease occurs before the age of 60, and is rare compared to the late on-set disease. In most cases it has a genetic cause; some have non-genetic causes, and others are due to another dementing disease.
Not all people diagnosed with Alzheimer’s Disease actually have the disease.
About 30 to 50% of people diagnosed with Alzheimer’s in life are found, after death, to have another dementia altogether. Autopsy is the only way to confirm the diagnosis. Most misdiagnosed cases have a preventable form of dementia called small vessel disease of the brain, or vascular dementia. This dementia is caused by poor cardiovascular health that damages the blood vessels of the brain.
So, high cholesterol, diabetes, heart disease, smoking, and high blood pressure are all major risk factors for this form of dementia. However genes are not.
Sometimes other dementia types also get misclassified as Alzheimer’s Disease, such as that associated with Parkinson’s, or rare forms involving the frontal lobes. When evaluating genetic risk, this misclassification matters. If you have a relative with Alzheimer’s Disease, there is no guarantee that the diagnosis is definitive, unless it is actually confirmed by autopsy.
If late-onset Alzheimer’s Disease is not highly genetic, can I positively impact my own risk?
Even with a high genetic risk, you can positively affect your chances of the symptoms of cognitive decline. Your lifestyle choices can have an additive effect on the likelihood that a genetic risk for Alzheimer’s will actually express itself during your lifetime. So, you may be able to decrease, and conversely, increase, your risk by your activity level, diet, wellbeing, sleep, and health.
Behaviors known to increase the risk of cognitive decline and Alzheimer’s Disease include:
1. Irregular exercise
2. Eating processed and nutrition-poor food
3. Leading a high-stress life with no relaxation or down-time (especially for women)
4. Sleep deprivation
5. Increasing levels of cholesterol, blood pressure and weight
6. Spending your time on passive, non-stimulating tasks (TV watching, repetitive routines)
7. Dependency on bad health habits (smoking, drinking)
8. Ignoring your brain health
For most of us, these damaging behaviours are more important than our genetic risk because they may amplify underlying susceptibility, and accelerate brain aging.
The bottom line:
Making brain-healthy choices every day could reduce your chances of cognitive decline, no matter what your genetic risk may be. When it comes to behavior change, today is always the best day to start making your brain health a priority.