Does Dementia Run In Families? Genetics And Other Risk Factors
If you’ve witnessed the effects of dementia on a parent or relative, you might be concerned about the possibility of developing the same disease. Scientists have made significant strides in recent years in their understanding of how genetics affect these neurocognitive disorders. Here, we’ll review what is known so far about how family history can influence your dementia risk.
The many types of dementia
There’s no simple answer to the question “Does dementia run in families?” That’s partially because dementia isn’t just one illness. Instead, it’s a collection of symptoms involving the progressive loss of major cognitive abilities like memory, sense of identity, language use, social cognition, reasoning, and orientation in time and space. This type of decline can be caused by many different kinds of brain diseases or injuries.
The most common forms of dementia (listed in descending order of prevalence) are:
- Alzheimer’s disease: a generalized loss of cognitive abilities due to atrophy of the brain caused by plaques and tangles of proteins in and between neurons
- Vascular dementia: the loss of cognitive functioning due to neurotoxicity from damaged or disrupted blood vessels in the brain
- Lewy body dementia, or dementia with Lewy bodies: a decline in brain function resulting from abnormal protein deposits that disrupt brain cell functioning and deplete crucial neurotransmitters
- Frontotemporal dementia (FTD): a progressive change in personality and loss of behavior and/or movement control caused by neuronal damage in the brain’s frontal and temporal lobes
Rarer causes of dementia include infections, traumatic injuries, and certain substances.
Is Alzheimer’s genetic?
Alzheimer’s disease is the most widespread type of dementia, currently estimated to affect around 3–4% of older adults. This condition most commonly appears in people over the age of 65, though some rare and aggressive cases can occur at younger ages.
Genetic testing can’t tell you for certain whether you’ll develop Alzheimer’s. That said, researchers have found that a family history of this illness does increase a person’s risk. The more family members with Alzheimer’s disease you have, the greater the chances of developing it yourself.
The absolute increase in risk resulting from genetic factors is usually relatively small. Some estimates suggest that a family history of Alzheimer’s disease could raise the baseline risk from 2–2.6%. This is less than the increase in risk incurred by simply aging 10 years.
Genetic studies have discovered some specific risk genes. Some suggest that mutations in at least 75 locations on the human genome may increase a person’s chances of developing Alzheimer’s disease. Each one only slightly changes the odds, but the more high-risk genes an individual carries, the greater their likelihood of developing the disease.
Familial Alzheimer’s disease
Certain rare variants of Alzheimer’s can be directly inherited from parents. Researchers have identified three specific genes that are strongly predictive of this disease when mutated:
- Amyloid precursor protein (APP)
- Presenilin 1 (PSEN1)
- Presenilin 2 (PSEN2)
All three of these genes are believed to be involved in the formation of amyloid-beta, the protein fragment that builds up into neurotoxic plaques in the brains of people with Alzheimer’s. An individual with a mutated version of even one of these genes has a roughly 50% risk of developing young-onset Alzheimer’s disease. This is a more rapidly progressing version of the illness that can appear in a person’s 30s or 40s and can dramatically reduce their life expectancy.
Since this is an autosomal dominant disorder, the children of someone with early-onset Alzheimer’s disease are also at a much higher risk than the general population. They have a 50/50 chance of inheriting the gene responsible for the disorder. These genes are quite rare, though: The familial variant makes up only about 5–6% of all cases of Alzheimer’s.
Is vascular dementia genetic?
Vascular dementia is usually not passed down through families. Instead, this condition can be caused by a diverse array of problems with the brain’s network of blood vessels. Some of these causes are associated with inherited risk factors, but most don’t have a single, well-defined genetic cause.
Here are a few examples of the many things that can contribute to vascular dementia risk:
- High blood pressure
- Strokes
- Smoking
- Atrial fibrillation (irregular heartbeat)
- A sedentary lifestyle
- Diabetes
- High cholesterol
- Atherosclerosis (hardening of blood vessels) in the brain
- Chronic stress
All of these risk markers result from a mix of genetic and environmental factors. For example, even behaviors like smoking may be influenced by genetics.
While studies have located some specific genes that may raise an individual’s risk of vascular dementia, they generally aren’t genetic “smoking guns.” A person may have multiple risk factors without developing this disease.
Strongly inherited vascular dementia
Certain rare types of vascular dementia result from mutations in a single risk gene, making them highly heritable. For example, the disease known as CADASIL results from a variant of the NOTCH3 gene that thickens the walls of the brain’s small and medium-sized blood vessels. This can cause repeated small strokes, leading to early-onset dementia along with many other neurological problems. Most people with this disease inherit it from a parent. These highly heritable forms of vascular dementia are very rare. CADASIL is believed to affect less than one-tenth of one percent of the population.
Is Lewy body dementia genetic?
Estimates of the heritability of dementia with Lewy bodies (DLB) range from as low as 30% to nearly 60%. While the science may not be settled on this question, most researchers agree that genetic factors play at least a partial role in the development of this form of dementia.
Families including multiple DLB patients appear to be quite rare. However, a family history of Parkinson’s disease (PD), Alzheimer’s disease, or other forms of dementia are known risk factors for this illness. This may indicate that some of the genetic factors that can contribute to AD or PD may also lead to DLB under certain circumstances.
Recent genomic studies have identified several apparent shared risk factors for DLB, Alzheimer’s, and Parkinson’s:
- APOE ε4. It produces a malformed version of apolipoprotein E, which helps with cholesterol transportation.
- GBA variants. Several mutated versions of the gene for glucocerebrosidase, a protein involved in cell membrane construction, may contribute to dementia.
- SNCA variants. This gene codes for the protein alpha-synuclein, which is the central component of the damaging protein clusters that interfere with brain cell function in Lewy body dementia.
Is frontotemporal dementia genetic?
Research suggests that between 20–50% of frontotemporal dementia (FTD) cases can be classified as “familial FTD.” These individuals appear to develop the disease due to a mutated gene passed down from parent to child. Most familial FTD can be explained by changes in one of three genes:
- MAPT. This gene codes for the tau protein, which can form damaging tangles inside brain cells.
- GRN. Mutations here lead to malformation of the progranulin protein, which can result in an unhealthy buildup of the related protein TP-43 in brain cells.
- C9ORF72. This protein is found throughout the body but may play an important role in synaptic connections between neurons.
There are also many non-familial cases of FTD. They may be influenced by genetic risk factors, but they lack clear genetic causes.
What should you do if you have a family history of dementia?
Although having family members with dementia can increase your risk, there may also be things you can do to protect your long-term neurocognitive health. Adopting certain healthy lifestyle behaviors may reduce the risk of Alzheimer’s and other forms of dementia in many cases. Examples include:
- Quitting smoking
- Getting regular physical exercise
- Avoiding heavy alcohol consumption
- Eating nutrient-dense foods as often as possible
- Managing your blood pressure, blood sugar, and cholesterol
- Engaging in intellectually stimulating activities
- Finding healthy outlets for stress
These behaviors are likely healthy for most people, and they might be additionally beneficial if you know you have a high genetic risk of dementia.
If you are struggling with substance use, contact the SAMHSA National Helpline at (800) 662-4357 to receive support and resources. Support is available 24/7.
Proactively addressing mental health challenges might also help you avoid cognitive decline. For instance, some research indicates that depression might be a modifiable risk factor for Alzheimer’s disease. Consulting a mental health professional if you’re experiencing symptoms of a mental health condition like this could have a protective effect.
If you’re not sure how you can fit in-person therapy into your schedule, you might consider online mental health care through a platform like BetterHelp instead. Web-based therapy sessions may be more flexible, and since you can participate from anywhere with an internet connection, you may find regular attendance easier. A 2020 research review found no difference in effectiveness in treating depression between face-to-face and internet-delivered cognitive-behavioral therapy.
Takeaway
Genetics can affect your risk for all forms of dementia, but the influence is often relatively small compared to other factors. Some varieties do consistently run in families, but they’re very rare. Adopting healthy habits may help offset a genetic risk of dementia.
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