Inevitably, whenever the words “lifestyle” and “designer babies” are used in a report on genetic screening or embryo testing, free rein is given to speculation on the more repulsive fantasies of Aldous Huxley's hatcheries and Nazi eugenics. The ethics of human reproduction and scientific intervention in this delicate area are a moral minefield, provoking strong emotions and a cacophony of opinions. It is not surprising, therefore, that the decision by the Government's fertility watchdog to allow a couple to test their embryos for a gene that causes high cholesterol levels is as controversial as it is misunderstood. It appears, at first glance, to open the way to designing children who will never grow fat or to speeding the acceptance of bioengineering to produce superbabies. It is no such thing.

The procedure that has been allowed by the Human Fertilisation and Embryology Authority is designed to detect a rare version of a disease called familial hypercholesterolaemia (FH), which often kills children before puberty. The condition occurs in two forms — a relatively mild one, caused by a single mutated copy of a gene, that nevertheless raises cholesterol levels to dangerous levels, causing heart disease, hardened arteries and strokes; and a far more deadly version, when the sufferer inherits two defective copies that cause high levels of cholesterol from the age of 5, angina and likely early death.

The principle of screening embryos to avoid such suffering has already been accepted for such conditions as Huntington's disease and cystic fibrosis. Other diseases, caused by genetic defects, have recently been added to the list. This pre-implantation genetic diagnosis, using embryos obtained by IVF, screened and then re-introduced to the womb, is costly, invasive and must be regulated by clear guidelines. But there is no reason why FH should be excluded. It does, however, raise a moral dilemma: while embryos with double mutations should not be implanted, what should be done with those affected by only the milder condition? Should parents — and the State — be obliged to support the birth of a child who will, inevitably, face a life of some suffering and much expense? Or should even partially affected embryos be discarded and the mother obliged to undergo again the full IVF procedure?

Several clear principles must be paramount when framing a moral and legal response. The first is that the parents should decide. The circumstances of each case may differ. Only parents can judge what they and their offspring are prepared to undergo. Secondly, medical regulation remains essential. Sanction for pre-implantation diagnosis does not apply to other situations: abortion of a foetus in the womb is a very different issue that raises other ethical questions. Thirdly, the scientific possibilities of screening must not be abused. Parents who choose this rigorous and sometimes distressing procedure over natural conception do so out of determination not to pass on genetic defects. They are not trying to manipulate their genes to raise IQ, breed a top athlete or “design” a baby — nor could they, when limited by their own gene pool. But a technique to prevent suffering must never be used for eugenics, with a promiscuous shopping list of genes to be screened out. That way not only moral madness lies, but present fears of Frankenstein science could prove all too true.