Humans easier to clone: US study

DURHAM - A genetic characteristic that sets primates apart from other mammals makes humans technically easier to clone than sheep, cows and mice, says an American study.

Humans, apes and monkeys possess two functional copies of a gene that helps to regulate foetal growth, meaning cloned babies are protected from foetal overgrowth, which has plagued animal cloning efforts, say scientists at Duke University, in North Carolina.

In this so-called large-offspring syndrome, many cloned mammals grow abnormally big in the womb and generally die just before or after birth. These clones also have under-developed lungs and reduced immunity to disease.

"It's going to be probably easier to clone us than it would be to clone these other animals because you don't have this problem - not easy, but easier," says Randy Jirtle, professor of radiation oncology and senior author of the study, which appears in the journal Human Molecular Genetics.

But cloning experts call the conclusions faulty.

"The authors have allowed themselves to over-interpret their interesting results," says Ian Wilmut, director of the Roslin Institute in Scotland, who in 1996 created the world's first cloned animal, Dolly the sheep.

"I hope this will not be used to give encouragement to those who wish to clone humans."

Two groups of scientists have announced plans to create the first cloned human babies, despite concerns about deformities.

Jirtle, molecular evolutionist Keith Killian and other Duke researchers traced the history of a gene called insulin-like growth factor II receptor (IGF2R) in a variety of mammals. A key function of the gene is to dampen a chemical that stimulates foetal growth.

The researchers say that about 70 million years ago, late in the age of dinosaurs, the ancestors of today's primates evolved a genetic idiosyncrasy relating to this gene.

Nearly all non-primate mammals inherit only one functional copy of the gene because of a rare phenomenon known as genomic imprinting, in which the function of the gene is turned off.

But humans and other primates possess two activated copies of the gene, with their offspring receiving one copy from the mother and one from the father.

Cloning creates a duplicate of an organism that is virtually identical genetically. But when scientists manipulate the fledgling embryos during the cloning process, the way gene IGF2R functions can be altered, leading to complications such as foetal overgrowth.

Humans and other primates have the built-in safeguard of two functional copies of the gene, the researchers say.

Since no primate has been cloned, the theory is untested.

Wilmut says that while gene IGF2R "is a candidate for some of the problems in cloned sheep, it is certainly not the only one."

Mouse cloning researcher William Rideout, who has made key contributions to animal cloning technology, agrees.

"From everything we've looked at, the overgrowth phenotype in the mice cannot be attributed to a single gene or even a single pathway so far," he says.

"It looks much more like a sort of random disregulation across many genes."

- REUTERS

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