Science: The Truth About ... Designer Babies

THE PHRASE "designer babies" means different things to different people. To some it smacks of eugenics, to others an ideal means of ridding humanity of inherited illnesses. The idea that we can now alter a person's genes is becoming embedded in the public consciousness. However, the fact is that at present, despite millions of pounds spent on various projects, scientists have not yet successfully altered the DNA of humans to cure a single genetic defect.

"Gene therapy" is the scientific term given to the procedure of trying to replace the faulty genes of a patient with a genetic illness with a healthy, working alternative. Most of the research has been done on animals, with the eventual aim of treating people carrying a potentially fatal mutation of a single gene. A classic example is cystic fibrosis, where a person who has two flawed copies of the CF gene suffers a condition where their lungs produce too much mucus.

The first problem scientists attempting gene therapy face is: how do you introduce the new gene into the cells which need it? In the case of CF, the important cells are in the nose and lungs. Research in the United States has focussed on adding copies of the working CF gene to cold viruses (since they invade the nose and lungs, and make the cells generate their proteins - including that of CF). In Britain, efforts have focussed more on delivering the genes via fat molecules called lipids.

But neither method has yet cured a patient. Adding a gene to a cell that is part of a working, living body is far more complicated than creating a transgenic animal: in the latter, the gene is added to an embryo outside the womb, which is then re-implanted and allowed to mature.

Even then, not all attempts succeed. A couple of years ago a more radical idea for performing gene therapy was suggested: use a weakened form of a retrovirus, which inserts its DNA into that of the cell it invades. If it inserts a healthy gene, that can't be bad. There are some dangers to this approach: the virus may become harmful again, or perhaps it might incorporate genetic material into the patient's reproductive, or "germ" cells, which make sperm in men and eggs in women.

The idea that gene therapy could affect the germ cells - and so pass on any changes to the patients' descendants - has raised some of the greatest ethical concerns about the technology. In Britain, anyone proposing a gene therapy trial must also show that the additional gene cannot be passed into the germ line. In CF patients, this means only performing the trials on men, because their illness also renders them sterile.

This restriction also prevents scientists trying gene therapy on foetuses or embryos, which would be an "infinitely easier" means of adding a gene, to quote Leroy Hood of the University of Washington, Seattle. "We have terrific ways to do that," he adds. Those embryos would grow up into people with the new genes in every cell of their body. Those in favour of such "germ-line gene therapy" say it means we might be able to eradicate genetic diseases for good and so choose how we evolve.

For the moment, such research is outlawed because of the many scientific uncertainties surrounding what would happen if gene therapy was performed on germ-line cells. Designer babies will remain an ingredient of science fiction for some time to come.

Charles Arthur