Chinese scientists have inserted a gene in monkeys that causes an extremely rare autism syndrome in people.

The mutant monkeys show unusual features in their first few years of life, including anxiety, abnormal social interactions, and running in circles around their cages, as described on Monday in the journal Nature.

The monkeys took six years to develop, and their care costs up to 50 times more than laboratory mice, the scientists said. Experiments on monkeys are also more ethically fraught.

But researchers are increasingly disillusioned with mouse models of brain disorders. The vast majority of studies of experimental drugs are done on rodents, and about 90% of those drugs fail when actually tested in people. (Just this month, pharma giant Novartis reported the failure of two clinical trials of a touted autism drug that had reversed symptoms in mouse models.)

“We think this non-human primate is absolutely required, in the long run, for our development of therapies and drugs for human psychiatric and neurological disease,” Mu-ming Poo, director of the Institute of Neuroscience at the Chinese Academy of Sciences in Shanghai, where the new monkey work was carried out, said at a press briefing. “There seems no other choice.”

Autism’s diverse array of social and communication problems is difficult, if not impossible, to fully model in any animal. And the new mutant monkeys diverge from the human syndrome in important ways.

Still, independent scientists told BuzzFeed News that making the monkeys was an impressive technological feat. And these animals — long-tailed macaques — are far closer to us on the evolutionary family tree than mice are.

“For me, it’s not even a question that one should study primates versus mice in this context,” said Partha Mitra, a professor at Cold Spring Harbor Laboratory in New York, who is working on brain-mapping projects in both mice and monkeys.

