Autism may carry a benefit: a buffer against Alzheimer’s

Brain plasticity of people with the developmental disorder may protect them from dementia

Having autism may protect people from Alzheimer’s. The idea, described June 17 in Medical Hypotheses, is preliminary and will require many more experiments before scientists know if it’s correct.

The concept is intriguing, says molecular biologist Cara Westmark of the University of Wisconsin-Madison. “Looking at connections between autism and Alzheimer’s disease is really exciting,” she says. “Both disorders are showing skyrocketing levels just in the past decade.”

Two curious trends led neuroscientists Alvaro Pascual-Leone of Harvard Medical School and Lindsay Oberman of Brown University’s medical school to the idea that autism spectrum disorders might protect against Alzheimer’s. The researchers focused on brain plasticity, the ability of the brain to change in response to incoming information. The changes can include strengthening connections between nerve cells or rewiring neural highways. Earlier studies have shown that the brains of people with Alzheimer’s have low brain plasticity, while people with autism seem to have high brain plasticity.

To explore this difference Pascual-Leone and Oberman used a technique called transcranial magnetic stimulation to give a little jolt to the motor cortices in the brains of 35 people with Asperger’s syndrome, a form of autism, and of 35 people without the disorder. Electrodes measured hand responses to the jolt. On average, the hands of people with Asperger’s syndrome were more responsive to the stimulus than those of people without Asperger’s. The larger response indicates higher levels of brain plasticity.

This heightened plasticity seems to decline with age. Plasticity was lower in the older subjects in the study, regardless of whether they had Asperger’s, than in the younger ones. But by starting with higher plasticity, people with autism might never reach the very low levels of plasticity associated with Alzheimer’s, the researchers propose.

The people with Asperger’s syndrome in the study had normal IQs. Scientists don’t know how the brains of people with other forms of autism, including those with intellectual disabilities, would perform.

A search of Harvard-affiliated hospital records failed to find many patients over the age of 55 who had been diagnosed with both Alzheimer’s and any type of autism. The search results turned up fewer than 10 cases, the default minimum returned by the search algorithm, suggesting that such cases are rare or nonexistent. 

That dearth could be explained by non-biological factors, Pascual-Leone says. Decades ago, doctors were less likely to diagnose someone with autism regardless of symptoms, and people are less likely to be diagnosed as adults. Another possibility is that finding signs of the mental decline that comes with Alzheimer’s may be particularly hard in people with autism, especially for those who might already be functioning at a lower intellectual ability, Westmark says.

“It’s a really novel idea, that autism could be protective,” she says. However, she adds, “I think that someone could probably write an equally convincing paper on the opposite.”

In fact, her research and others’ have hinted that certain forms of autism increase a person’s risk of Alzheimer’s, perhaps by changing the levels of the protein fragment amyloid-beta, which is thought to be involved in Alzheimer’s.

More studies will help sort out the relationship between the two disorders, says Pascual-Leone. He and colleagues hope that such a link will ultimately point to ways to ease symptoms of both diseases. “The implication of this is why I find it tantalizing,” he says. Exercise, medications and cognitive training may all have the potential to change brain plasticity, he says.

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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