- WASHINGTON (Reuters) - Cloned
mice have hundreds of abnormal genes, which explains why so many cloned
animals die at or before birth and proves it would be irresponsible to
clone a human being, scientists said.
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- The process of cloning introduces the genetic mutations,
and there seems no immediate way around the problem, Rudolf Jaenisch and
colleagues at the Massachusetts Institute of Technology reported.
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- "I think this confirms suspicions that I have always
had and that many others had that cloning is a very inefficient method
at this point," Jaenisch said in a telephone interview.
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- "It is very irresponsible to think this method could
be used for the reproductive cloning of humans."
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- Even before Dolly the sheep became the first mammal to
be cloned from an adult cell, in 1997, researchers have known that cloning
is difficult.
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- The most common cloning method is called nuclear transfer
and involves taking the nucleus out of an egg cell, replacing it with the
nucleus from a cell of the animal to be cloned, and then "reprogramming"
the creation so the egg begins dividing as if it had been fertilized by
a sperm.
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- Only one of every several hundred eggs ever start dividing
and of these, only a small percentage result in pregnancies. Many of the
animals that survive to birth die soon after, or develop abnormalities
of the lung, liver and other organs.
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- Jaenisch and colleagues at MIT's Whitehead Institute,
working with Ryuzo Yanagimachi of the University of Hawaii, who was the
first to clone mice, made dozens of cloned mice and then looked at the
activity of 10,000 genes using a gene chip.
-
- Writing in this week's issue of the Proceedings of the
National Academy of Sciences, they looked mostly at the placentas of the
newborn mice, long assumed to be the source of the problem, but also at
the livers of some of the clones.
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- GENE CHIP SHOWS ABNORMAL GENES
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- They found many abnormal genes. The pattern was so clear
that they could tell normal mice from cloned mice by looking at the results
of the gene chip study, they reported.
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- "There is no reason in the world to assume that
any other mammal, including humans, would be different from mice,"
Jaenisch said.
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- He said the finding should convince anyone who doubted
the danger of trying to clone a human, referring to last summer's debate
between he and other cloning experts, and three scientists who said they
planned to try to clone human babies to help infertile couples.
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- "It settles the old question ... about how normal
can clones be," Jaenisch said.
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- The three scientists have each said they are on the verge
of creating a cloned baby but none has produced evidence that convinces
scientists such as Jaenisch.
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- The issue has been debated in the U.S. Congress and competing
bills would outlaw attempts to clone a human being, and some would outlaw
using cloning technology in human beings at all.
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- Several cloning researchers have said their cloned livestock,
such as cattle, sheep and pigs, are normal and healthy if they get past
birth.
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- Jaenisch believes genetic abnormalities will be found
even in these seemingly normal animals. Some of the abnormalities are simply
not fatal, he said.
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- Many of the problems the team found were in so-called
imprinted genes, involved in the development of the embryo. In the imprinting
process only the copies of a gene that a baby gets from its father are
turned on.
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- "Almost 50 percent of those were incorrectly expressed,"
Jaenisch said.
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- That may mean that so-called therapeutic cloning, which
uses cloning technology to make human cells for use in medical treatments,
would be safe, he said.
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- "In therapeutic cloning you don't form an embryo,"
Jaenisch said, noting it went to an early stage of development in which
a ball of about 100 cells is formed.
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- "In cloning most, if not all, problems arise during
embryonic development," he added.
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