Designer-baby doctors make trouble for a living. But they weren't prepared for this...

When Uri Verlinsky got up to address the fertility experts assembled for the Third International Symposium of Pre-Implantation Genetic Diagnosis held in Bologna, Italy, in June, he was nervous. He knew he had ground-breaking results to present. He did not anticipate how controversial they would be.

When Uri Verlinsky got up to address the fertility experts assembled for the Third International Symposium of Pre-Implantation Genetic Diagnosis held in Bologna, Italy, in June, he was nervous. He knew he had ground-breaking results to present. He did not anticipate how controversial they would be.

A decade ago, Dr Verlinsky, a world-renowned molecular geneticist based at the Illinois Masonic Medical Center in Chicago, pioneered with the British expert Alan Handiside the technique of genetic screening for embryos that has transformed the outlook for couples with inherited disorders. By identifying and discarding embryos carrying the defective gene in the laboratory, scientists can now give affected couples a near guarantee that they can give birth to a healthy child.

About 2,000 children worldwide have been born using the technique, 1,100 of them at the Illinois Masonic Medical Center, which leads the world. But what Dr Verlinsky had to present to the fertility experts in Bologna were the first results from a new method for tissue-typing embryos to match them with existing siblings.

His presentation was based on the case of the Nash family of Colorado, whose six-year old daughter, Molly, suffers from the rare genetic illness Fanconi anaemia, which is invariably fatal. Treated at the Illinois centre, by a team led by Charles Strom, director of medical genetics, they had conceived a son who was not only free of the inherited disorder but had also been selected from the 12 available embryos to be the best tissue match for Molly so he could provide a transplant of stem cells taken from his umbilical cord to treat and, potentially, cure her disease.

Fertility experts who heard Dr Verlinsky's address were initially aghast. Paul Serhal, medical director of the in-vitro fertilisation (IVF) unit at University College Hospital who was at the meeting, said Dr Verlinsky was "lambasted. The pre-implantation diagnosis community were very against this idea because they consider it a slippery slope. It was a typical kneejerk reaction. He was given a very rough time," Dr Serhal said.

Two months later, Adam Nash was born in Denver, Colorado, on 29 August, a healthy boy and a potential saviour for his sister. Doctors stored blood from his umbilical cord, which is rich in stem cells and is normally discarded at birth.

Four weeks after his birth, on 26 September, the stem cells were infused into Molly's circulatory system. Doctors are now waiting to see whether the transplant has been successful.

As the extraordinary story of the Nash family has unfolded in the world's media over the past few days, fertility experts have rapidly revised their view of the ethics of the procedure. From initial revulsion and warnings of children being seen as "commodities", conceived to benefit others, a new view is emerging that this represents the best use of medical technology to alleviate human suffering.

Here was a family with a dying child who wanted a second child who would be unaffected by the same disorder. They opted for IVF with pre-implantation genetic diagnosis (PGD) to avoid selecting embryos with the defective gene, and as a bonus, used tissue typing to select the best match for Molly.

The case is a mirror image of the Siamese twins, Jodie and Mary, where one has to die so the other may be saved. In the Nash family's case, Adam's conception could be the saving of Molly.

Mr Serhal, of University College Hospital, London, said: "One should not look at this case as an ethical disaster. One should look on it as an example of what can be done. They are not creating a baby to use it for spare parts. The couple wanted to have a healthy child and they chose IVF because if they had conceived naturally there would have been a risk the baby would have been affected. Matching the baby to be compatible with his sister was a bonus, a spin-off. It was a double hit."

He was backed by Simon Thornton, medical director of the Care IVF Unit at the Park Hospital, Nottingham. "I think this is the absolutely appropriate application of leading-edge technology. The couple obviously didn't want another affected child. A new technique comes along that can prevent that and as a bonus it has the potential to help [the] older sibling."

Mike Macnamee, director of operations at the Bourn Hall IVF clinic in Cambridge, said: "You can ask if couples should have the right to select embryos against a genetic abnormality. But once they have done that the use they have put the cord blood to is excellent."

The Human Fertilisation and Embryology Authority (HFEA) is in the middle of a consultation exercise on PGD. Its discussion document, which has been sent to a wide variety of interested organisations, considers just about every ethical issue except the one resulting from the selection and birth of Adam Nash.

The consultation recognises that PGD will result in new ethical dilemmas as a result of being able to test IVF embryos before they are implanted into the womb.

The HFEA has already dealt with the ethics of selecting male and female embryos, judging that gender selection can only be allowed for sex-linked disorders and not merely because parents wish to have a boy or a girl.

Another issue is whether the widespread availability of PGD will affect peoples's attitudes towards disabled people and their families "by creating a climate where genetic disability is increasingly seen as preventable", the consultation document says.

The HFEA says it is opposed to using PGD in order to select embryos for "social or psychological characteristics, normal physical variation, or any other conditions which are not associated with disability or a serious medical condition". However, its document accepts that there may be some groups, such deaf people, who may wish to use PGD to selectembryos that are affected by the same inherited condition as themselves to bring up children who are more like their parents.

Another ethical dilemma is whether in the course of testing an embryo for one genetic condition, another disorder becomes apparent. "If the couple concerned felt that this was their opportunity, they may choose to have the affected embryo replaced anyway, rather than lose the chance of having a child altogether," the consultation report says. "The question therefore arises whether it is right deliberately to cause a child to be born with a disability?"

PGD will also enable doctors to detect embryos suffering from "late onset" disorders. Sometimes late-onset conditions can occur in middle age, which means that affected people can have 30 or 40 years of normal life.

Another potential problem arises when PGD is used to test for a genetic predisposition, such as an inherited tendency to develop heart disease or cancer.

The question then is whether it is right to test for a condition that may either be preventable or may never occur in that person's lifetime.