Autism and Dementia: (1) Prevalence

- Hello, where are you?

- I am at home.

- At home? Where?

- I have one home, in England. Why? What’s happened?

- Why did you leave without saying ‘goodbye’? It was great when you and your daughter came to see me. We visited friends and had fun. I was preparing your farewell party, but you left. You could have said goodbye…

Thus began my conversation with my childhood friend (B.). We have been in contact with him all our lives, despite living in different countries – thousands of miles away from each other. First, we wrote letters and then skype each other regularly. A few weeks before this conversation, I couldn’t get through to him on skype – there was no answer. It was very unusual. And then there was that phone call from him. To say that it was a blow for me is to say nothing: the matter is, the last time we visited him was more than 10 years ago…

In his teens, B. was diagnosed with Asperger syndrome (now ASD-1). With a sharp mind and original thinking, he was popular with both his university friends and lecturers. Academically, B never experienced problems: he got PhD in History, worked as a school teacher and then as an university lecturer. His personal life, however, wasn’t so successful: married and divorced three times, at the age of 60 he ended up living alone.

Up to this point, if I came across the research articles on autism and dementia, I never thought that it could become my personal interest and desire to learn as much as possible; it was just one of many other topics to be aware of.

Currently, though growing, the research on the intersection between autism and dementia is still limited.

What we know about prevalence of dementia in autism:

The findings are controversial, for example:

Barnard-Brak et al. (2019) examined the comorbidity with Alzheimer’s disease and any form of dementia in individuals with ASD from 1999 to 2015. Their results indicate that autistic individuals were, in fact, less likely than the general population to have Alzheimer’s disease or any form of dementia. However, males with ASD were significantly more likely to have acquired Alzheimer’s disease or a form of dementia as compared to females with ASD.

These data seem to confirm the findings of Oberman & Pascual-Leone’s study (2014) that autistic individuals might be relatively protected from age-related cognitive decline and the risk of dementia due to the brain hyperplasticity (excessive amount of plasticity) of some autistic individuals. Plasticity is essential to the establishment and maintenance of brain circuitry; however, too much plasticity may lead to instability of structural connections and compromise of functional systems necessary for cognition and behaviour. Oberman & Pascual-Leone hypothesize that individuals whose cortex begins as relatively “hyperplastic” (such as may be seen in ASD) should then be relatively protected from age-related cognitive decline (which, they suggest, is related to a reduction in plasticity). Oberman & Pascual-Leone have that an individual’s risk of age-related cognitive decline (and risk for manifesting symptoms of dementia) depends on the individual’s starting point and slopes of change in plasticity efficiency over the lifespan.

However, other studies demonstrate that middle-aged autistic adults have increased risk of dementia, greater longitudinal hippocampal volume loss and are more likely to show clinically meaningful decline in short-term memory, compared with non-autistic adults. The research findings suggest a key memory brain structure, the hippocampus, may shrink faster over 2-3 years compared with non-autistic population, and short-term memory may become more challenging for some. Across a broad adult range, autistic adults also had reduced integrity of connections to the hippocampus and greater challenges with long-term memory (Pagni et al. 2022).

Klein et al. (2022) found high rates (30%) of cognitive decline. The most common symptoms were declining interest in leisure activities, and increases in everyday problems with thinking, memory, and judgment. There was evidence that autistic women may be more vulnerable to cognitive decline than autistic men. Notably, reports of cognitive decline did not vary by age or educational level.

According to Vivanti et al. (2021) who examined the nationwide prevalence and incidence of Alzheimer's Disease and other types of dementia in ASD in autistic adults aged 30-64 years in the US during 2008-2012, 4.04% of autistic adults were diagnosed with early-onset dementia, compared with 0.97% of non-autistic adults. Interestingly, the prevalence amongst people with both autism and intellectual disability (ID) was 5.22%, which is lower compared to individuals with ID only (7.10%).

More questions than answers:

If autistic people are relatively protected (due to brain hyperplasticity) from age-related cognitive decline and the risk of dementia, why is the prevalence of dementia significantly higher in autistic people than in non-autistic people?

Are individuals with ASD and ID/learning disability more protected from dementia than those with ID/learning disability but without ASD?

Are autistic men or women more vulnerable to cognitive decline and more likely to develop Alzheimer's or any other form of dementia?

So far, so confusing.