Embryo selection critics fear 'slippery slope'

At the heart of the controversy surrounding Pre-implantation Genetic Diagnosis (PGD) is that age old ethical terror, the "slippery slope".

The main objection to the procedure is that it opens the door to a world of nightmarish possibilities.

As technology races on, there is no telling where it will stop, say the critics.

If embryos can be selected to be free of harmful genes, they argue, who is to say they will never be screened for particular genetic traits that parents might desire or want to avoid?

Enter the "designer baby" who is destined to be top of the class, excel in sport, and have hair, eyes and other physical characteristics that fit his or her parents' wish list.

Alternatively, deaf or blind couples might want their disabilities passed on to their child. Some members of the deaf community who claim they belong to a "linguistic minority" are already campaigning for the right to have hearing-impaired children.

The Human Fertilisation and Embryology Authority's decision in 2006 to allow PGD to target genes for breast, ovarian and bowel cancer intensified the "slippery slope" debate.

Critics saw this as an unwelcome slackening of the rules, a dangerous step forward down the "designer baby" road.

Cancer genes were different because, unlike other disorders screened out by PGD, they did not inevitably affect the individual carrying them. Although the risk might be quite high, there was a possibility of not developing the illness.

Also, unlike genetic conditions such as cystic fibrosis or Huntington's disease, these cancers could be cured if caught early enough. By permitting the selection of embryos free of cancer genes, the PGD bar had been lowered.

PGD has also ushered in the concept of "saviour siblings" - children grown from "healthy" selected embryos so that their cells can be used to treat a brother or sister with an inherited disease. For some, this practice is immoral and abhorrent.

Against these arguments is the fundamental principle that if treatments or procedures exist that can vanquish serious diseases, it is immoral not to use them.

Advocates of PGD reject the "slippery slope" fear, insisting there is no danger now or in the future of embryo selection producing a super-race of designer babies.

They say careful use of PGD has the potential to eradicate serious inherited diseases that have plagued families for generations.