National Geographic

We may not be alone in our struggle against Alzheimer’s disease. For the first time, the plaques and tangles that characterise the condition have been found in the brains of elderly chimpanzees, although it is unclear if they cause dementia in the animals.

In the brains of people with Alzheimer’s, a protein called beta-amyloid accumulates and forms sticky plaques between brain cells. These plaques trigger changes in another protein called tau, causing it to form tangles. Together, these plaques and tangles are thought to kill brain cells, leading to dementia.


It is difficult to study the disease and develop treatments for it because other species seem not to develop plaques and tangles. The only time they’ve both been seen in another animal’s brain was in a 41-year-old chimpanzee, but they were thought to be the result of a stroke.

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But Melissa Edler, now at Northeast Ohio Medical University, and her colleagues have had the rare chance to study 20 brains from older chimpanzees, aged between 37 and 62. The team examined four areas of the chimps’ neocortex and hippocampus – brain regions most commonly affected by Alzheimer’s in humans. They discovered beta-amyloid plaques and early forms of tau tangles coexisting in 12 of the chimp brains and, as in humans, they saw increasingly larger volumes of plaques in the chimp brains of more advanced age (Neurobiology of Aging, DOI: 10.1016/j.neurobiolaging.2017.07.006).

It is not clear whether these plaques and tangles lead to the same kind of cognitive decline in chimps that we experience. “Our samples had been collected over decades, without any consistent or rigorous cognitive data accompanying them,” says Mary Ann Raghanti of Kent State University, Ohio, in whose lab the work was performed. “So it wasn’t possible to say whether the chimps had devastating cognitive loss or not.”

However, so far, there are no examples of chimps with Alzheimer’s-like dementia. “I’m cautious to say that they don’t get this kind of devastating decline, but we haven’t seen it yet,” says Raghanti.

This study contributes to growing evidence that the classic plaques and tangles of Alzheimer’s disease may be by-products rather than the cause of the disease, says Gary Kennedy, director of the Division of Geriatric Psychiatry at Albert Einstein College of Medicine in New York. “That great apes demonstrate the pathology but not the precipitous decline of dementia reinforces this notion.”

Humans may have something unique about their brain that predisposes us to the cognitive decline that accompanies plaques and tangles, says Raghanti. “If we can identify those differences between the human and chimp brain then we might be able to pinpoint what is mediating the degeneration. That could be a target for drug treatment.”

This article will appear in print under the headline “Chimps show signs of Alzheimer’s”