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Wednesday, 8 August, 2001, 11:56 GMT 12:56 UK
Q&A: Human cloning
At what stage are attempts to carry out human cloning?
American fertility specialist Panos Zavos and Italian embryologist Severino Antinori are at the centre of the heated debate on human cloning. They say they intend to produce human clones as a way of helping infertile couples have children.
The plan has provoked outrage on moral grounds - and experts in the field doubt whether the men can achieve their intentions.
Dr Zavos and Dr Antinori recently appeared before an investigative committee of the US National Academies to try to convince them that the use of cloning to help childless couples is both practically and ethically acceptable.
It is widely suspected that other scientists around the world may also be experimenting with human cloning, but Dr Zavos and Dr Antinori are the chief public advocates of the practice.
Where can Dr Zavos and Dr Antinori carry out the cloning attempt?
Although the practice might infringe laws in many countries, not all nations have taken the step to specifically ban human reproductive cloning. The UK has - although it does allow limited cloning to develop new cell therapies - and the US is going the process of doing so at the moment.
The medical authorities in Italy are considering withdrawing Dr Antinori's licence to practice medicine if he pursues his experiments.
He says he may carry out the process in an unnamed Mediterranean country or on a boat in international waters to avoid these restrictions.
How would cloning be achieved?
The model is Dolly the sheep, a clone produced by British scientists in 1997. Although the technology has been applied to several animals, it is still underdeveloped and the mechanisms involved are poorly understood.
The process involves removing the DNA from the nucleus of an egg cell taken from the mother.
This genetic material would then be replaced by the DNA taken from one of the father's cells - perhaps a skin cell. An electrical trigger would be applied to the egg cell, which would make it start to divide like any normal embryo. It would then be implanted in the mother's womb in a procedure that is routinely performed in infertility clinics.
Drs Zavos and Antinori may have the equipment to attempt human cloning. They say they have about 1,500 volunteers.
The techniques required are all recorded in precise detail in scientific journals, but the technology is poorly understood and fraught with dangers for both the mother and the child.
So what are the dangers?
Experience with the five mammal species that have been cloned so far indicates a low chance of success.
The vast majority of pregnancies involving clones have gone very badly. In most of them, the clone has died and in almost all of them the lives of the mother and clone have been put at risk.
In many cases, the clone grows abnormally large, often threatening to tear the womb, which can also become swollen with fluid. Almost all clone pregnancies spontaneously abort.
Dolly the sheep, the first mammal clone, was the first success in 247 pregnancies.
What are the prospects for a human clone?
Of the small number (little more than 1%) of animal clones that survive the gestation period, most have severe abnormalities - malfunctioning livers, abnormal blood vessels and heart problems, underdeveloped lungs, diabetes, immune system deficiencies and possibly hidden genetic defects.
Several cow clones had head deformities and none survived very long.
But Zavos and Antinori claim to be able to "quality control" embryos choosing only "healthy" ones?
At this stage, screening for suitable embryos is not expected to work.
Normal babies are made from the joining of genes from sperm and egg. Genes are "imprinted" - a poorly understood process that avoids any genetic confusion between similar maternal and paternal genes.
There is evidence that in clones this imprinting does not work properly. At present there is no way to screen any embryo to detect this problem.
What about long-tern health?
We know very little about the long-term health of clones.
There is some evidence that they may not live as long as conventionally conceived animals and may have health problems. Studies are ongoing.
Would the child be an exact copy of the genetic parent?
No. On the genetic level, the clone would be 99.9% identical to its parent. It would not be a complete copy because there are some important genes that would be contributed by the egg donor. These genes reside outside the nucleus.
Also, the clone would be subject to different environmental factors and a different upbringing to his/her genetic parent. This could result in a changed appearance and personality.
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