The world's first monkeys with customised genetic mutations have been born at a university in China.
The twin cynomolgus monkeys were successfully engineered by Xingxu Huang, a geneticist at the Model Animal Research Center of Nanjing University.
Both were born with two targeted mutations using a system that has wide implications for the field of genetic engineering.
Researchers say their achievement means we are now a step closer to making more realistic models of human diseases.
Mice have long been used as models for human diseases because they reproduce quickly and in large numbers. However, this research was always unfeasible on monkeys because of their slow reproductive system.
Hideyuki Okano, a stem-cell biologist at Keio University in Tokyo, told Nature Magazine: "We need some non-human primate models."
The researchers tested the engineering technology in a monkey cell line and found three genes that had a success rate of between 10 and 25%.
Following this, they targeted the genes into over 180 single monkey embryos, which resulted in 10 pregnancies. One of these led to the live birth of the monkeys with two mutations.
One of the mutations is involved in regulating metabolism, while the other is to do with healthy immune function.
The mutations do not represent any specific disease, although both are associated with human disorders. The researchers believe their success could lead to targeting human conditions that have multiple mutations. "There are a lot more things to do," Huang said, adding they are now awaiting the results from eight other pregnancies.
Commenting on the study, Rudolf Jaenisch, a stem cell researcher from the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, said that while the results are interesting, it is still far from providing any answers to genetic mutations.
"The next step is to see if we can learn anything from it," he said.