Cloned animals are genetic misfits, MIT scientists find
CAROLYN ABRAHAM, MEDICAL REPORTER
Friday, July 6, 2001
They're often so fat and deformed they endanger their surrogate mothers while in the womb. They're prone to breathing troubles and dying young.
Now scientists have found that cloned creatures also suffer a range of other problems invisible to the human eye.
A team of U.S. scientists studying 38 cloned mice has found that even clones that look healthy carry genetic glitches which could lead to physiological defects.
While such abnormalities were not severe enough to result in miscarriages or stillbirths, scientists suspect that these defects could wreak havoc with organs and even trigger foulups in the brain later in life.
The findings provide further evidence that cloning a human being is a dangerous idea. But they also cast a sobering light on a field in which scientists are anxious to clone embryonic stem cells to grow human tissue and organs for transplant.
"We feel it's unlikely that you can really ever create a normal clone," said David Humpherys, the molecular biologist who led the research at the Whitehead Institute for Biomedical Research at the Massachusetts Institute of Technology.
"With our existing technology, it seems unlikely that we can actually generate identical copies."
A steady parade of sheep, cows, goats, pigs and mice have been cloned in the world's laboratories over the past few years. But it is estimated that for every 100 cloning attempts fewer than five result in live births.
Those that survive tend to be obese and suffer circulatory problems.
It had been generally presumed that clones were genetically healthy if they made it to term.
Instead, Dr. Humpherys said, "The few successful animals are not really healthy or normal animals; they are just the ones [clones] with the fewest problems."
Cell biologist Samuel Weiss, chairman of the Genes and Development Research Group at the University of Calgary, said the new research represents a cautionary tale for scientists such as himself who hope to clone stem cells to grow tissue and organs for transplant in human patients.
Working with scientists at the University of Hawaii, the MIT researchers, whose report appears today in Science magazine, cloned 38 mice using two methods.
In one process, they transferred the nuclei of embryonic stem cells into mice eggs that had their genetic material removed (a method similar to that which created the famous cloned sheep Dollie).
In the second process, researchers coaxed an embryonic stem cell itself to grow into an embryo.
Then the scientists implanted the clones into the wombs of surrogate mice mothers and on the last day of the pregnancies, removed them by cesarean section.
Next, researchers studied a subset of so-called imprint genes in the cloned mice.
Dr. Humpherys said he was surprised at the range of genetic "instability" despite the fact that they had created the clones from embryonic stem cells. These primordial cells have generated huge excitement since they have the ability to become any tissue and organ that constitutes a living body.