Rare Types and Symptoms of Alzheimer’s

Reviewed by: HU Medical Review Board | Last reviewed: May 2023

Alzheimer’s disease is the most common form of dementia. Its symptoms usually affect people’s thinking and behavior, most notably their memory. Alzheimer’s progresses to the point where people with it need help to perform daily tasks and activities.1

But there are some kinds of Alzheimer’s, and some symptoms, that are rarer than others. While these types of Alzheimer’s are uncommon, they still affect many people and are important to look out for.1-6

Early-onset Alzheimer’s disease

Alzheimer’s disease is most common in adults over age 65. But it does sometimes affect people younger than this. When this happens, it is known as early-onset or younger-onset Alzheimer’s disease. There are 2 main types of early-onset Alzheimer’s disease:1-3

  • Common early-onset
  • Familial or genetic early-onset (discussed in the next section)

It is believed that Alzheimer’s is caused by proteins accumulating in plaques and tangles in the brain. According to this theory, the plaques and tangles harm the cells in the brain. Everyone develops plaques and tangles as they get older. But people with early-onset Alzheimer’s develop more of them earlier.1

It is not known why some people get more plaques and tangles. And it is not known how these cause Alzheimer’s for some people. The only currently known risk factor for early-onset Alzheimer’s is family history.1

Familial autosomal dominant Alzheimer’s

Familial autosomal dominant Alzheimer’s (FAD) is a type of early-onset Alzheimer’s. FAD is caused by mutations in genes that run in families. There are 3 genes where mutations are known to cause FAD:2,3

  • Presenilin 1, the most common
  • Presenilin 2
  • Amyloid precursor protein

If a parent has a gene for FAD, each of their children has a 50 percent chance of inheriting the faulty gene. The children of a person with FAD could be all affected, all unaffected, or a mixture. FAD affects the sexes equally. It does not skip generations. FAD symptoms usually start when someone is in their 30s, 40s, or 50s. By contrast, Alzheimer’s is normally diagnosed around age 65.3

Other rare types of Alzheimer’s

One to 3 of every 20 people with dementia have a rare, inherited, or early-onset diagnosis. Two other rare types of Alzheimer’s are:4,5

  • Frontal variant Alzheimer’s disease (fvAD)
  • Posterior cortical atrophy (PCA)

FvAD causes more behavioral symptoms and issues with a type of thinking called executive function. Executive function is the ability to concentrate on, plan, and complete tasks. People with fvAD may become less sympathetic or motivated. They may behave in socially inappropriate ways.4

PCA causes issues with visual processing in addition to normal Alzheimer’s symptoms. Visual processing is how you interpret what you are seeing. Someone with PCA may have trouble with:4

  • Recognizing people or objects in photos
  • Judging distances accurately
  • Using digital technology
  • Communicating

Rare types of Alzheimer’s have some similarities to more common types. But people with these rare types often require different resources and care. Talk to your care team about the best way forward if you suspect your loved one has a rare type of Alzheimer’s.5

Reduplicative paramnesia

Reduplicative paramnesia is a rare symptom of Alzheimer’s. The exact features and symptoms are still being discussed. But most doctors agree that people with reduplicative paramnesia believe that an environment (or objects) has been duplicated. Or they believe that they themselves exist in 2 places at the same time.6

If your loved one experiences reduplicative paramnesia, talk to your care team about how to manage this symptom.6

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