Unlike typical Alzheimer’s disease (the non-inherited form) which usually occurs in people in their 70s or 80s, FAD usually occurs much earlier. People with FAD typically first develop symptoms before the age of 65, most commonly in their 40s or 50s. However, this varies considerably between different families. In some families, individuals may be as young as their early 30s when they become affected.

The initial symptoms of FAD are usually similar to those of typical Alzheimer’s disease – primarily memory loss. The memory problems in Alzheimer’s disease are different from everyday forgetfulness. Importantly, they are ‘progressive’, meaning that they become worse over time. They are also different in that in FAD, other people are usually more aware of the memory problems than the person experiencing them. Over time, the memory problems in Alzheimer’s disease spread to affect other forms of thinking such as new difficulties with planning or performing calculations. Symptoms can be hard to detect, but a clear sign is a distinctive and progressive decline in abilities.

It is important to note that many people in families with FAD worry about their memory – and understandably so – but most of the time this is not an indication that they have developed FAD.

Sometimes FAD is referred to as autosomal dominant Alzheimer’s disease (ADAD). This is a different name to describe the same condition.

Causes

Familial Alzheimer’s disease (FAD) is a rare form of Alzheimer’s disease caused by faults (known as mutations) in genes that run within families. Mutations in three genes are known to cause most cases of FAD. These are the presenilin 1 (PSEN1), presenilin 2 (PSEN2) and amyloid precursor protein (APP) genes. A mutation in PSEN1 is the most common of these three to cause FAD.

This means that in each family the disease is caused by a mutation in a single gene and that a single copy of the mutated gene, inherited from one parent, will cause the disease. The onset of symptoms in FAD occurs usually at a relatively young age, usually 30s, 40s, or 50s and other family members may also have been affected at a similarly young age.

Most commonly Alzheimer’s disease (AD) is not familial and is not caused by a genetic mutation.

In most cases, the relatives of someone who has Alzheimer’s disease have no greater risk of getting Alzheimer’s disease than anyone else. This is a very different situation to what occurs in FAD, where the disease is entirely caused by inheriting a faulty gene.

How likely am I to inherit FAD?

If someone has one of the gene mutations that cause FAD, then each of their children has a 50% chance (1 in 2 chance) of inheriting the faulty gene. Each sibling of someone with the faulty gene will have had a 50% chance of inheriting it.

An affected parent could have all children affected or unaffected, or a mixture of both. FAD affects males and females equally and does not skip generations. However, it may appear to skip a generation if a person with the faulty gene dies of another cause before symptoms develop.

Individuals with familial Alzheimer’s disease usually have a strong family history of the illness, which means that, as well as one of their parents, they know of cousins, aunts/uncles and grandparents who were affected at a similar age and who belong to the side of the family of their affected parent. In some cases, an individual may not know whether they have a family history of Alzheimer’s disease, for example if they do not know their biological parents or if their parents died young.

As far as we know, if an individual is tested and has inherited one of these faulty genes, then they will almost certainly go on to develop Alzheimer’s disease at some point in their life. They are also highly likely to develop symptoms around the same age that their parent developed them. This means if you are a lot older than an affected parent and do not have problems then you are unlikely to have inherited the genetic mutation and your children are not at risk.

Genetic testing and counselling

If someone has a relative with Alzheimer’s disease and is concerned about whether it may be familial, they should gather as much information as they can about their relative’s family history so that they can discuss it with the doctor caring for their relative. The doctor will also be able to refer them to a specialist genetic counselling service if appropriate to discuss their concerns and arrange genetic testing if needed.

The results of any genetic test have important implications not only for the person being tested but also for the rest of the family. It is important to discuss these carefully with a specialist who has expertise in genetic counselling, before any genetic tests are performed.

A genetic test for FAD can be performed on a blood sample and is usually done because several other family members have Alzheimer’s disease. However, it may also be performed when symptoms or brain scans suggest familial Alzheimer’s. For more information on the different types of genetic testing and counselling for FAD, please visit the I think I am at risk of FAD. What next? page.

You can find out more about genes and typical Alzheimer’s disease by visiting the Alzheimer’s Research UK website. One of our members has shared their journey undergoing genetic counselling and testing for FAD. You can read Jess’ story.

You may also find visiting our FAQs section useful.

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