A family of genetically modified monkeys with glowing green feet have been created by Japanese scientists in an experiment that could advance research into diseases such as Parkinson’s and Huntington’s.

Although GM monkeys have been born before, the marmosets are being regarded as a scientific milestone because they are the first to have passed a genetically engineered trait from one generation to the next.

The achievement raises the possibility of colonies of GM monkeys being bred for use in medical research. Scientists avoid experimenting on primates when possible, but they remain the best available animal models for studying many conditions, especially brain disorders and infectious viruses such as HIV.

It may now be possible to breed monkeys with mutations causing them to develop diseases such as Huntington’s and motor neuron disease, enabling scientists to study their progress and to develop treatments.

The research has raised ethical concerns because it could lead to an increase in the number of experiments on primates. Some research groups said, however, that the use of GM monkeys could reduce the number of animals needed because they provided better models for human disease.

A team led by Erika Sasaki, of Keio University, inserted the green fluorescent protein (GFP) gene into 91 marmoset embryos using a modified virus, and 80 of these were transferred to surrogate mothers.

The experiment led to the birth of five offspring, named Hisui, Wakaba, Banko and twins Kei and Kou. Keikou means “fluorescent” in Japanese. Kou’s sperm was then used to fertilise eggs by IVF, resulting in the birth of two more GM marmosets with skin on the soles of their feet that glows green under ultraviolet light. One survived, but the other died after being bitten by its mother. The research is published in the journal Nature.

“The successful creation of transgenic marmosets provides a new animal model for human disease that has the great advantage of a close genetic relationship with humans,” the researchers wrote.

Gerald Schatten, of the University of Pittsburgh, who led the team that created Andi, the first GM primate, in 2000, and Shoukhrat Mitalipov, of the Oregon National Primate Research Centre, said: “The birth of this transgenic marmoset baby is undoubtedly a milestone. The cumbersome and often frustrating process of making a transgenic animal from scratch need now only occur with founder animals.” They pointed out, though, that marmosets were not as useful as rhesus macaques or baboons for modelling some human diseases.

Kieran Breen, director of research and development at the Parkinson’s Disease Society, said: “This is potentially very exciting for the future of research into the causes of Parkinson’s disease.” Simon Festing, the chief executive of Understanding Animal Research, said: “Ethical evaluation and public engagement are vital to maintain confidence in such research.”

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