Humans 'easier to clone than sheep or mice'

Humans could be easier to clone than sheep, cattle or mice, according to scientists who have found that a crucial technical hurdle to the procedure does not exist for people.

Humans could be easier to clone than sheep, cattle or mice, according to scientists who have found that a crucial technical hurdle to the procedure does not exist for people.

One of the biggest arguments against human cloning is that it would be too risky to attempt, but a study by a team of scientists in the United States has shown that these fears could be overstated.

The researchers found that, unlike sheep, cattle, pigs and mice, where cloning results in a high number of foetal deformities and birth defects, humans possess an unusual genetic trait that mostly protects them from this risk.

The findings, which are published today in the journal Human Molecular Genetics, could help to undermine the arguments of critics of human cloning, who say that the procedure is far too unsafe given the high proportion of cloned animals that are born defective.

Keith Killian, a member of the team from Duke University Medical Center in Durham, North Carolina, said: "This is the first concrete genetic data showing that the cloning process could be less complicated in humans than in sheep."

The work centred on a gene for a protein called insulin-like growth factor 2 receptor (IGF2R), which is known to be critical for the growth and normal development of an embryo in a womb.

Cloned sheep and cows are known to suffer from "large offspring syndrome", where foetuses grow far bigger than normal, resulting in a high proportion of stillbirths and other developmental abnormalities.

Scientists believe that this happens because the IGF2R gene is not functioning. Although sheep, cattle and most other mammals have two copies of this gene, only one of them is switched on. However, in some cloned animals, even this single functioning gene is switched off due to a complicated genetic phenomenon known as imprinting.

However, the Duke University researchers have found, humans and other primates do not share this imprinting trait with other mammals. In man, both copies of the IGF2R gene are switched on, suggesting that all clones would have at least one functioning gene, therefore making it theoretically likely that human cloning would be technically easier and safer.

Dr Killian said: "Only one in 300 sheep embryos takes hold, and up to half of these embryos have large offspring syndrome, which can kill the mother and the foetus. Since humans are not imprinted at IGF2R, then foetal overgrowth would not be predicted to occur if humans were cloned."

Randy Jirtle, another member of the Duke University team, believes that the findings will lend weight to those who believe that human cloning should be allowed to proceed.

"It means that the cloning of humans will be easier – not easy – but easier. The technical issue against it might not even be there. This moves on from whether we can clone people to whether we should clone people," Dr Jirtle said.

He added: "If you ask me whether I want cloning, I don't want to see a mini me because I've got two fine children the old-fashioned way. But it's up to to society to choose."

The Duke University study used data from the Human Genome Project to show that imprinting does not affect the IGF2R receptor gene. The American scientists also analysed genetic data from man's nearest relatives, and discovered that this trait is shared by other primates – but not by other mammals.

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