Humans are the only animal known to develop Alzheimer's disease, and an official diagnosis requires checking off this list of three things: dementia, which is observed through screenings, and two pathologic markers—amyloid plaques (sticky bunches of misfolded proteins) and neurofibrillary tangles (tau proteins clumped together and twisted around). While amyloid plaques have been found in several species of aging primates, the tau tangles found in people have never been spotted outside of humans—until now. Reporting in the journal Neurobiology of Aging, researchers say they've discovered them in our closest relative, the chimpanzee.
Since chimps were declared endangered in the US in 2015, research on them has been dramatically restricted, and invasive research is banned, making MRI scans on aging chimps unlikely. But a new center that obtains the brains of chimps who died at zoos or research centers enabled this study, reports Science. Twenty brains that belonged to chimps who'd died between the ages of 37 and 62 (the latter is about 120 in human years) were analyzed; 13 had amyloid plaques and four of those had tau tangles. Still, chimps don't display severe dementia. "They're missing something," an outside neuropathologist tells Scientific American. It's possible the proteins are folded differently to protect them, which has the potential to inform human treatment. At the very least, they're the only other animal known to display Alzheimer's pathologic signature. (Many people being treated for Alzheimer's may not have it.)