A few facts about genetics, testing and young onset dementia

Some forms of young onset dementia have clear genetic links. Others do not. Here is some information about some of the most prominent gene links and genetic testing options.

Lab workers looking at gene diagrams

In recent years, researchers have made progress in identifying some of the genes associated with young onset dementia.

At the same time, there have been an increasing number of people who are interested in finding out about their genetic risk for young onset dementia.

Here are key facts to be aware of if you are starting to learn about genetic aspects of young onset dementia.

This article also includes some tips about the process of getting genetic tests for young onset dementia done in Canada.

Some forms of young onset dementia have clear genetic links; others do not.

“Young onset dementia” is a term that covers dozens of different diseases and conditions.

Some genetic mutations are dominant and have a high penetrance—meaning they generate disease with a high degree of certainty.

Other genetic mutations might increase the risk of someone developing young onset dementia, but do not make it a certainty.

And other kinds of young onset dementia lack a clear genetic link.

If you want to read more about some of the research into genetics and young onset dementia, check out the list created by Young Onset Dementia UK.

Under Canadian law, you do not have to disclose your genetic results to your employer or insurance company—or almost anyone else, really.

On May 4, 2017, the Genetic Non-Discrimination Act became law in Canada.

This law prohibits any person from requiring an individual to undergo a genetic test or to disclose the existing results of genetic tests.

Essentially, almost nobody is allowed to collect, use or disclose your genetic test results without your written consent. And even if they collect it, they are not allowed to discriminate against you because of your results.

You are also entitled to get a genetic test without having to consent to further disclosures that are not directly related to providing you with the service that you want.

(The main “service” you might need to disclose your genetic results for would be those related to specific medical treatment or related drug therapies, trials and care.)

Two of the main young onset dementias that have clear genetic links include Down syndrome dementia and Huntington disease dementia.

Down Syndrome occurs when a person is born with an extra copy of chromosome 21. This chromosome carries the gene for amyloid precursor protein. And this gene helps create certain Alzheimer’s disease substances in the brain.

According to the World Alzheimer Report 2021, “virtually all adults with Down syndrome develop the hallmarks of Alzheimer´s disease pathology by age 40, and the lifetime risk of dementia is estimated to be well over 90%.” For more information, read our related infosheet.

Huntington disease is a brain disorder caused by a mutation of the gene HTT, which is found on chromosome 4.

According to the Huntington Society of Canada, “Symptoms usually appear between the ages of 35 and 55, but the disease can appear in youth (under 20 years – Juvenile HD) or older adults (Late Onset HD).”

Huntington disease is highly genetically inherited. If a parent has HD, then their biological child has a 50% chance of also having the HTT gene mutation and therefore developing HD as well. More information on the dementia that can come with Huntington disease is available in our infosheet.

In some young onset frontotemporal dementias, multiple genes have been identified.

Some strong genetic links have also been identified for certain kinds of frontotemporal dementia (FTD). About 40% of the people who develop FTD have a family history of the illness.

C9orf72 is the most common genetic mutation in hereditary FTD.. The GRN Progranulin mutation and the MAPT Microtubule-associated protein tau mutation are also prominent in hereditary FTD.

According to some research, someone who inherits the GRN Progranulin mutation, for instance, has a 60% chance of developing frontotemporal dementia by age 60.

Researchers continue to examine other genetic factors for frontotemporal dementia.

A few different gene mutations can also increase the probability of young onset Alzheimer’s disease.

The gene mutations best known to be associated with young onset Alzheimer's disease are: Amyloid precursor protein (APP) on chromosome 21; Presenilin 1 (PSEN1) on chromosome 14 and Presenilin 2 (PSEN2) on chromosome 1.

The National Institute on Aging says that “A child whose biological mother or father carries a genetic mutation for one of these three genes has a 50/50 chance of inheriting that mutation” for young onset Alzheimer’s disease.

As in many areas of ongoing scientific research, there are other factors to consider, too: In 2017, the journal Frontiers in Molecular Neuroscience published research indicating that “PSEN1 changes account for approx. 80 % of young onset familial Alzheimer’s disease, and PSEN2 account for approx. 5% - not sure if we want to add more information.”

Research continues on whether other genetic factors exist. And discoveries are ongoing. In April 2022, for instance, a group of researchers discovered 42 new genes associated with Alzheimer's disease in general, doubling the number of genes known to be connected to this illness.

If you are interested in genetic testing, it’s best to see a genetic counsellor.

Before genetic testing, it’s important to know exactly what kind of young onset dementia might run in your biological family.

It’s also important to understand what role, if any, genes play in that particular kind of young onset dementia.

The good news is: you don’t have to figure these things out all by yourself.

A genetic counsellor is a health professional who can help you know these important facts.

Genetic counsellors are also very up to date on what the latest testing research, genetic science findings, and practical testing options are.

And genetic counsellors also help people figure out whether they are ready to pursue a genetic test. They review the pros and cons of finding out a genetic result, and help you assess your need to know.

Genetic counselling is usually free as part of Canada’s healthcare system; just ask your doctor for a referral

Because genetic counselling is part of our national healthcare system, it usually comes at no extra cost—unless you are going through a private clinic.

All you have to do to get connected for free is to ask your doctor or nurse-practitioner to refer you to a genetic counsellor.

You can also find a genetics clinic close to you by using the index on the website of the Canadian Association of Genetic Counsellors.

This helpful video from the Canadian Association of Genetic Counsellors also explains a bit more about what genetic counsellors do.

Free genetic counselling and/or testing is also sometimes available through research studies or drug trials.

There are some research studies and drug trials going on right now worldwide that focus on genetically linked young onset dementias, or that look at young onset dementias that run in families.

All those studies and trials need participants in order to proceed. Sometimes they are specifically looking for participants who are gene-positive due to family history but who not symptomatic yet. Hence, their offers of free genetic testing.

As a result, some people in Canada can, from time to time, access to genetic counselling and/or testing by applying to a young onset dementia research study or drug trial.

Naomi Mison, who lives in Kamloops and is founder of Discuss Dementia, found that going this route was the right choice for her.

“Initially when I talked to a doctor about genetic testing, I was told that ‘Unless actively pursuing having children, we would advise against getting the test’ Naomi recalls. “Then, for a time, I didn’t pursue it further, because I didn’t have a need to know.”

“But as time went on, I learned a bit more about clinical research. I knew that as a child of somebody with a younger onset dementia, there is an increased likelihood of developing the disease,” Naomi says. “And I realized that information is power. And I would rather know what I'm up against than not. Because I believe you have an opportunity to take preventative or corrective stuff, or engage in related trials.”

“So later, is also where other routes came in,” Naomi concludes. “A local facility here was offering some testing for free because a study was trying to find participants, so I did testing that way.”

A list of dementia research studies currently looking for Canadian participants is available at alzheimer.ca/joinresearch.

Avoid direct-to-consumer genetic tests

In Canada, there are an increasing number of options for direct-to-consumer genetic tests—meaning tests like 23andme and AncestryDNA.

These types of kits are not good options for getting tested for young onset dementia risk.

“With an unsupervised, at-home test, there is a real possibility of misunderstanding results, which could result in making misinformed decisions about your health,” the Alzheimer’s Association notes.

Leah, who recently got her genetic results through a research study, started on her genetic testing path with a genetic counselling appointment many years ago—and sees the benefits of having this kind of professional advisor on hand when going through the process.

“I had a desire to know my results right away,” Leah says, “but then the counsellor led me through a range of implications that knowing the results could have on my mindset and lifestyle given some of my pre-existing medical conditions. They took a full medical history from me to understand those implications, too.”

Leah continues: “Though I eventually felt ready to find out my results from a research study participation 13 years later, under the supervision of a neurologist, those first steps with the genetic counsellor were essential. It was also really important for me to talk to my other doctors about wanting to get tested—to have support in pursuing testing, and also in knowing resources were in place for me for emotionally processing the results.”

For more information and support, contact your local Alzheimer Society.

Your local Alzheimer Society can help you get oriented to the genetic counsellors and genetic testing clinics in your area.

The staff at your local Alzheimer Society can also direct you to more information about young onset dementias that run in families. And they can help connect you to other organizations and resources in your area that might be helpful.

To connect, find information for your local society at alzheimer.ca/find. Or call or email our national office at 1-855-705-4636 and info@alzheimer.ca to get linked up with your area office quickly.