Gene defects emerge in all animal clones

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"Gene defects emerge in all animal clones"

 

Jonathan Leake Science EditorThe Sunday Times (London)http://www.biotech-info.net/gene_defects.html

A REVIEW of all the world's cloned animals suggests that every one of them is genetically and physically defective. Ian Wilmut, co-creator of Dolly the sheep, the first mammal to be cloned from an adult cell, published his findings this weekend.

The study coincides with claims by researchers trying to create the first cloned human. In Italy, Dr Severino Antinori has claimed that three women are pregnant with cloned babies; in America, Dr Panayiotis Zavos has said he will achieve such a pregnancy within two years.

Wilmut said his latest research suggested that a cloned human would also be at huge risk of genetic defects.

This was a clear warning that "nobody should be attempting to clone a child". The new study surveys cloning efforts worldwide. "The widespread problems associated with clones has led to questions as to whether any clone was entirely normal," Wilmut said.

Dolly, the sheep cloned by Wilmut five years ago at the Roslin research centre in Scotland, has already shown defects. She was born with chromosomes that have shortened telomeres the DNA tips that protect the end of chromosomes.

In normal sheep and humans telomeres grow shorter with age. As they shorten, cells seem to become more prone to disease and death. This has been linked with diseases of ageing and cancer. Earlier this year Dolly was found to be developing arthritis at a far younger age than is normal in sheep.

Wilmut listed defects occurring regularly in other cloned animals, including gigantism (excessive size) in cloned sheep and cattle; placentas of up to four times the normal size in mice; and heart defects in pigs.

Despite being given normal amounts of food, many cloned mice also become grotesquely fat, while many cloned cows, sheep and pigs have developmental difficulties, lung problems and malfunctioning immune systems.

Cloned animals have also shown a variety of individual defects. A calf cloned in France appeared to be thriving but suddenly died at 51 days old after a failure in its ability to produce white blood cells.

Similarly, scientists at Roslin had to put down a cloned lamb at 12 days old because the muscles around its lungs were so abnormally thick that it could hardly breathe.

Wilmut has looked at the behaviour of methyl molecules which attach themselves to DNA in all cells and help to control many of its functions.

He found that the methylation of the DNA in adult cells differed sharply from that of sperm and eggs. It means that when a nucleus is taken from a cell of an adult animal and injected into an egg the process that leads to a clone its DNA is formatted in radically different ways from that found in sperm.

He believes this is why the genes of cloned animals seem to behave in unpredictable ways and suggests that human clones are also vulnerable to this problem.

Earlier this year Advanced Cell Technology, an American company, announced that it had created three cloned human embryos but admitted that none had been able to grow to more than six cells in size.

Wilmut concludes: "There is abundant evidence that cloning can and does go wrong and no justification for believing that this will not happen with humans."

The researchers behind the human cloning programmes said they could overcome such problems. Zavos is seen increasingly as the more serious candidate. He claims to have two laboratories perfecting their techniques on animals before attempting to reproduce a human in the "near future".

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Last Updated on 5/14/02 Email: information