BAR HARBOR, Maine - New scientific evidence has heightened concerns about the safety of cloning human beings, an international authority warned yesterday.
“We now believe that the potential to make a normal human baby with cloning is almost zero,” said Dr. Rudolf Jaenisch, professor of biology at the Massachusetts Institute of Technology, at a genetics conference at Maine's Jackson Laboratory.
“Cloning a normal human is an illusion. There are major problems, and the problems are very serious.”
Dr. Jaenisch, who helped pioneer gene transfer and cloning, said the public continues to be enthralled by stories of maverick doctors who supposedly plan to clone human beings.
Italian doctors in Rome, for instance, claim that they will clone a baby by next spring, with $500,000 provided by a couple whose infant died after heart surgery. An American firm called Clonaid has made repeated claims about a imminent human cloning.
“Cloning a normal baby is utter nonsense,” said Dr. Jaenisch at the conference sponsored by Jackson Laboratory, Johns Hopkins University, and the March of Dimes. “The evidence from cloned animals shows that even apparently normal clones have subtle genetic abnormalities.”
The abnormalities occur as a side effect of cloning technology, which first produced a carbon-copy mammal - Dolly the sheep - in 1997.
Cloning animals involves manipulating the nucleus in a cell taken from an adult animal. Scientists transfer the nucleus to an egg cell whose nucleus is removed.
The egg then is implanted into the uterus of a surrogate mother. The mother eventually bears offspring that is a genetic carbon copy of the adult who donated the cell.
Dr. Jaenisch said the genetic errors result from the speed at which reprogramming of genes occurs. In humans, at least 30,000 adult genes would be reprogrammed to their embryolike condition in a brief period.
He described studies, done with scientists from the University of Hawaii, in which cloned mice were screened for genetic abnormalities. The research team found massive defects even in animals that appeared perfectly normal.
“Hundreds and thousands of genes are misregulated in cloned animals,” Dr. Jaenisch said. “It would be impossible to screen 30,000 genes for defects in human embryos cloned for reproductive purposes. Safe cloning of humans may never be feasible.”
Dr. Jaenisch challenged claims from commercial agricultural cloning firms that cloned cows and other farm animals are normal. The same genetic defects almost certainly occur in farm animals.
In cows, nobody cares about the defects so long as the animal produces a lot of milk, Dr. Jaenisch said.
In humans, however, those defects could translate into serious diseases and problems with behavior and intelligence.
The defects may explain why some cloned animals die younger, he said, noting that cloned mice have a life expectancy one-third shorter than naturally conceived mice.