Suzana Herculano-Houzel

Chimpanzees also have Alzheimer’s disease – now what?

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Alzheimer’s disease is not my thing, but we live so much now that it’s inevitable that the subject will end up being mentioned in other contexts. In circles that study the diversity of the nervous system and how the human brain compares to (or differs from) others, one statement was particularly common in lectures: “only humans suffer from Alzheimer’s disease”.

From the audience, I rolled my eyes and mentally grumbled. It is well known that the main risk factor for Alzheimer’s is advanced age. If the signs start on average around the age of 65, why would anyone expect rats and mice, who barely reach two years old, to suffer from this disease? Even monkeys, evolutionarily much closer to us and therefore better candidates to suffer from the same ailments, only live about 20 years.

I’ve been insisting for a long time that our species has nothing special apart from having invented cooking and thus overcoming the wall of energy limitation that applies to all the others, which only eat raw. That’s why, when a colleague asked me about human exclusivity when it comes to Alzheimer’s, my response was “is that really true? Has anyone ever examined whether elephants or whales, who live at least as long as elderly humans, really never show signs of Alzheimer’s?”. I then felt secretly vindicated when a colleague recently demonstrated that we are not alone in this respect either.

Mary Ann Raghanti, at Kent State University in Ohio, USA, who has been doing comparative studies of primate brains for a long time, obtained brain tissue samples from 20 chimpanzees who, raised in zoos or other institutions, lived much longer than the average of 33 years recorded in the wild. Fifteen animals died naturally at over 40 years old, and two at around 60.

Well: by different criteria, several of the 20 animals had the characteristic signs of Alzheimer’s disease, such as beta-amyloid plaques and Tau protein tangles. What’s more, both of the older animals had signs of advanced disease. Whether they also had the characteristic memory disorders and dementia is much more difficult to determine, as cognitive tests would have to be carried out on both young and old animals.

Therein lies an interesting problem for those opposed to animal research. Mice and rats are unlikely to provide a solution to Alzheimer’s; a new primate gerontology would have a much better chance of yielding results – but that requires studying monkeys and chimpanzees. So, is it worth it?

Originally published in Folha de São Paulo in December 2017

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