China has genetically engineered cloned monkeys to show symptoms of mental illness, including schizophrenia and depression.
The five macaques were born after cloning of the cells, after which the embryos were edited to remove the BMAL1 gene.
This has led to the manifestation of the features of mental illnesses caused by the destruction of their circadian rhythms, reveals a study in the National Review of Science.
They were edited with the same tool – CRISPR / Cas 9 – used by the Chinese scientist Ye Jianguy, who firmly claims to have created the world's first genetically modified human babies recently.
Unlike Mr He's experiment, the Chinese government has authorized and funded the monkey study conducted by researchers from the Institute of Neurology in the country.
Researcher Chan Hoon-Chun said discoveries could help develop treatments for human diseases ranging from diabetes and sleep disorders to neurodegenerative diseases and cancer.
Only China has a cloning technology for primates raised in captivity, with the first one born in early 2018, using the same technique that produces the sheep Dolly.
The latest study, however, raised further questions about the ethics of using a human-like species for such invasive research.
According to Alan Bates, Center for Animal Ethics in Oxford, the fact that the study is related to mental illness is "particularly controversial."
If the mental processes of the apes were "sufficiently close to humans to provide a valid model, then it would certainly be unethical to experiment them," he said.
He added that he could not see how lab animals "could not show symptoms close to mental illness."
Andrew Knight, a professor of animal welfare and ethics at the University of Winchester, said the study was "worrying" and "very irresponsible."
"Human mental illnesses are complex and even more difficult to predict from purely physical illness," he told the South China Morning Post.
"The probable benefit of damaging animals in this way is extremely small.
"However, there is no doubt that these animals will suffer – and probably many.
"Primitives are very intelligent and social animals, and it is not ethically intentional to harm them, especially when the chance for a tangible benefit to humans is so small, such research is very irresponsible."
Arthur Kaplan, a professor of bioethics at New York University, is divided by the study, saying the low cloning success rate has been "ethical in price" because there is a chance for deformed animals.
However, he said that if scientists are "competent," it is ethical to study human diseases on genetically-engineered animals that "you could not ethically try first in humans."