Famous German-born polar bear Knut died of an autoimmune disease of the brain previously known to only affect humans, new research has found.
He was lauded and loved by the public in Germany and across the world after being rejected by his mother and raised by zookeepers.
But five-year-old Knut drowned on March 19, 2011 after suffering epileptic seizures and falling into his enclosure's pool at the Berlin Zoological Garden.
Knut died of encephalitis, but the cause of the condition had been a mystery until now.
Researchers from German Centre for Neurodegenerative Diseases, Leibniz Institute for Zoo and Wildlife Research and Charité – Universitätsmedizin Berlin have solved the case, the results of which were reported in the journal Scientific Reports today.
They say it was a non-infectious illness called anti-NMDA receptor encephalitis, with symptoms in human patients similar to those Knut showed.
He is the first wild or domestic animal that has demonstrated signs of this form of encephalitis.
The authors of the study say the results could have wider implications for dementia patients.
"It is possible that autoimmune diseases of the nervous system might be far more common in humans and other mammals than previously assumed," Professor Alex Greenwood, Department of Wildlife Diseases head at the Leibniz Institute, says.
"We might underdiagnose autoimmune inflammations in human patients suffering psychoses or memory disturbances, because these patients are not routinely screened for associated antibodies."
That means patients might not necessarily get the best treatment and Dr Harald Prüß says there's a reasonable case to be made to examine patients for associated antibodies, especially if the cause of dementia is unknown.
Berlin Zoological Garden director Dr Andreas Knierim congratulated those involved in investigating the case, saying they've made it possible animals with a similar diseases can be diagnosed and treated earlier.