The controversial cloned sheep which provoked moral outcry last week suffered significant developmental problems and abnormally high birth- weights, it has been disclosed.
Three of the five lambs died shortly after birth and post-mortem analysis revealed congenital abnormalities in their kidneys and cardiovascular system. But a bigger blow to the much-trumpeted commercial prospects of the technology is the belated disclosure by scientists at the Roslin Institute near Edinburgh that all but one of the lambs were much larger than normal.
One lamb had to be delivered by caesarean section because it had grown to 6.75 kilograms - nearly twice the average birth weight of Welsh mountain sheep. The scientists did not disclose the details of the lambs' birth- weights when they reported the cloning in the scientific journal Nature last week.
But the high weights cast serious scientific doubt on the viability of the process. A very similar technique, employed to clone calves in the 1980s, had to be abandoned because one in five was larger than expected and one in twenty a giant - twice normal size. These calves were so large that the cows were physically incapable of giving birth to them.
The disclosure also makes it less likely that the Roslin technique could ever be applied to the cloning of human beings. The scientific limitations of the technique may make much of the fevered speculation last week about human cloning simply science fiction.
The Roslin team took a very early embryo from a Welsh mountain sheep and dissected out the cells destined to grow into lamb rather than placenta. They then cultured this "clone" of cells in the laboratory before implanting some into "foster eggs" - unfertilised eggs from which all the genetic code had been removed. The DNA of the cloned cell then took over and directed the development of the foster egg which was placed in the surrogate womb of a Scottish black-faced sheep.
The abnormal growth of the foetuses could simply be the result of being placed in the slightly larger surrogate Scottish ewes. But it appears more likely that the problems stem from the culturing or the foster egg stages or possibly both.
It may be that culturing the cloned eggs in the laboratory already accelerates their growth, and that fusing these cells with the foster egg provides them with double the resources normally needed for growth.
While the initial stages of any scientific development are experimental, the similarity with the overweight calves of the 1980s suggests that the limitations may be inherent to the technique.
A spokesman for animal rights campaigners, Compassion in World Farming, was reported yesterday as saying that it was appalling that the scientists had not revealed that the lambs were abnormally large.
When the news of the Roslin team's success in cloning the sheep first broke it sparked widespread fears over the cloning of humans. A Church of England spokesman warned the technology should be used with caution and that it would be "totally unethical" for it ever to be applied to people.
But Davor Solter, of the Max Planck Institute for Immunobiology in Germany, called the work "a cause for celebration".Reuse content