Will I inherit dementia from my parents? Is it hereditary?

If you’re caring for a relative living with dementia, it’s natural to be concerned about whether or not you or your children will develop the disease. In reality, there are actually different kinds of dementia – and most of them are not hereditary.

Read on to learn about the common types of dementia, and what the chances are for people with relatives diagnosed with dementia to develop the disease.

Understanding genetics

First, be aware that there are four common types of dementia – vascular dementia, dementia with Lewy bodies (LBD), frontotemporal dementia (FTD), and Alzheimer’s. Some types of dementia are more hereditary than others.

• Vascular dementia – Only in very rare cases can vascular dementia be caused by a genetically-inherited disorder.

• Dementia with Lewy bodies (LBD) – The Lewy Body Dementia Association (LBDA) explains how LBD is a term that covers two types of diseases: Parkinson’s and dementia with Lewy Bodies. Only about 10% of LBD cases are hereditary – and they are very rare.

• Frontotemporal dementia (FTD) – This is the second most common form of dementia among older people. It’s more likely that FTD can be inherited by other generations than vascular dementia, but FTD is still considered rare.

• Alzheimer’s – Alzheimer’s is the most common form of dementia, affecting 50-70% of all dementia patients. Of all of the four types of common dementia, researchers know the most about Alzheimer’s. Most types of Alzheimer’s disease are not hereditary, and the most common risk factor is age.

Second, it’s important to know about the role of genes when it comes to heredity.

Genes are the basic units of heredity that pass on characteristics like hair colour, height, or the tendency to inherent certain diseases.

They’re found in our chromosomes, and are frequently compared to thousands of beads on a string.

Women have 22 pairs of chromosomes in addition to two X chromosomes, and men have 22 pairs of chromosomes in addition to an X and a Y chromosome.

Genes can contain changes or mutations – and some of those mutations are beneficial while others are harmful.

Even if a gene that is associated with a particular disease is present in a person’s chromosomes, it needs to have the mutation or change that causes that disease. In other words:

• Some genes are “causative”. They actually cause a person to inherit a gene for specific illnesses. This means that the individual will develop the disease for certain.

• Other genes are “risk factor genes”. They won’t definitively cause or lead a person to develop a particular illness. However, depending upon the risk associated with that particular gene, they can indicate whether the person is more or less likely to inherit the disease.

Genes that may influence Alzheimer’s

The above-linked Alzheimer’s Society article is informed by responses from Professor Nick Fox, Honorary Consultant Neurologist at the Institute of Neurology in London. The article tells us:

• 99% of Alzheimer’s cases are not hereditary. And since the most significant risk factor is age, it’s not uncommon to have a parent or grandparent with Alzheimer’s disease who is in their late 70s and 80s. In that same 99% of Alzheimer’s cases, your risk of inheriting of Alzheimer’s compared to the rest of the population is very slight.

• In less than 1% of all Alzheimer’s cases, there is a very rare type that is hereditary. Early-onset Familial Alzheimer’s Disease, (eFAD), described here and here, affects between 2-3% of the population. If a physician diagnoses you with eFAD, one of your parents will have had the disease if they lived long enough. In addition, your siblings and children may have a 50-50 chance of inheriting eFAD. Note that early-onset Alzheimer’s usually occurs in individuals who are in their 30s, 40s or 50s. In rare cases, it occurs when a person is in their 20s.

• Researchers have discovered that certain genes will cause early-onset Familial Alzheimer’s Disease if they have a specific kind of mutation or change. Known as PS1, PS2 and APP, the full names of these genes are: Amyloid precursor protein gene APP on chromosome 21; Presenilin 1 on chromosome 14; and presenilin 2 on chromosome 1.

If early-onset Familial Alzheimer’s Disease is suspected

If your family has the gene that causes eFAD, you can receive predictive testing to determine if the gene has the mutation that causes the disease. In addition to predictive testing, you will always receive careful genetic counselling first.

If you suspect that there are cases of eFAD in your family (as opposed to other forms of dementia that are not hereditary) you need a thorough medical examination to know for sure. Also, if you suspect that someone in your family who is no longer alive had eFAD, their past medical records must be examined carefully.

In conclusion, having an elderly relative in your family that is diagnosed with Alzheimer’s does not mean that the disease will automatically be passed on to you or your immediate family members.

Which, as I mentioned earlier, less than 1% of Alzheimer’s cases are hereditary, meaning that they are instances of early-onset Familial Alzheimer’s Disease.

And for those cases that do carry the diagnosis of eFAD, there is counselling and genetic testing available to help you be prepared for a potential diagnosis should it be come back positive.