For years, scientists assumed all animals were prone to some cognitive decline as they age. Humans, though, were the only ones known to develop aging diseases that also come with a unique set of bodily changes. One of these is Alzheimer’s, a fatal form of dementia that starts with memory loss and progresses to a loss of lucidity and physical functions.
But in a paper published (paywall) Aug.1 in the journal Neurobiology of Aging, researchers found that 20 deceased chimpanzees all had changes in their brains typically associated with Alzheimer’s in people, making them the only other known animal to possibly share this disease.
Kent State University anthropologist Mary Ann Raghanti and her team conducted autopsies on chimps that had previously lived in zoos or research facilities, and had died in captivity between the ages of 37 and 62 years. (A chimp older than 60 is comparable to a human over 100 years old.) The research team looked specifically for the plaques and garbled blood vessels that are present in brains of people that have died of Alzheimer’s. They found tangles of blood vessels in all 20 chimps, and plaques in 13 of them.
“We can’t say these chimps had Alzheimer’s, but we can say for sure that they are the only other species with its pathologic hallmarks,” Raghanti told Science Magazine. None of the chimps exhibited specific signs of memory loss in their lives—or at least any that were recorded. It could be that these plaques don’t affect chimps the way that that they affect us, or that chimps have some other defense against the symptoms of the disease that we don’t. In addition, the plaques didn’t appear in chimps exactly the same as they do in humans. Humans who had Alzheimer’s tend to have these plaques floating around the tissue of areas associated with memory in the brain, and in the chimps, these were found in the blood vessels of the brain instead.
Raghanti told Nature she hopes further study of these deceased chimps’ brains will help scientists understand why the disease is so prevalent in humans. In 2016, there were roughly 44 million people worldwide diagnosed with Alzheimer’s, and the total number of people living with any kind of dementia is expected to be 131 million (pdf) by 2050. One major challenge for this line of scientific inquiry: medical research on live chimps is illegal in Europe, Japan, Australia, New Zealand, and in the US; in 2015 the US National Institutes of Health announced it would stop all formal research on chimpanzees. Chimpanzees are classified as critically endangered by the International Union for Conservation of Nature.