PARIS - A French couple has given birth to a healthy baby after losing two earlier children to a rare hereditary disease, thanks to the in vitro screening of embryos prior to implantation in the mother. This is the first time that such a technique has been successfully utilized in France.

The couple's two previous children had both died young after being born without an essential metabolic enzyme, ornithine carbamyl transferase (OCT). Because of the high risk of transmission of this condition and the fact that it is life-threatening and incurable, the couple was advised to conceive their third baby through in vitro fertilization (IVF), since the production of several fertilized embryos gives doctors the possibility of selecting a healthy one for implantation into the mother's womb.

The baby, Valentin, was born Nov. 13 at the Antoine-Beclhre hospital in the Paris suburb of Clamart. The doctors allowed the embryos to develop for three days before screening them. This involved extracting six or eight cells and examining them for genetic deformations using a range of reagents and genetic probes. The tests had to be conducted with great care, since the vast majority of such embryos do not survive in any case.

Following the birth, the doctors stressed that it was a perfectly normal baby like any other, and not genetically modified. They avoided accusations of indulging in eugenics by refusing to look at any other characteristics of the healthy embryo, such as its sex.

OCT is one of a small number of hereditary diseases caused by the mutation of a single gene for which France's 1994 bioethics legislation and related regulations governing medically assisted reproduction permit pre-implantation genetic screening. The others are Duchenne's disease (a form of muscular dystrophy), cystic fibrosis and spinal amyotrophia (Werdning-Hoffman's disease). Two others - myotonic atrophy (Steinert's disease) and X chromosome fragility - are due to be added to the list shortly.

In addition, pre-implantation diagnostic screening also is permitted for the purpose of looking for common chromosomal anomalies. These mostly involve so-called robertsonian translocations (where all or part of a chromosome is transferred onto a chromosome of another pair) and reciprocal translocations (where bits of DNA are interchanged between different chromosomes).

Since the end of July, the team that produced Valentin has conducted pre-implantation diagnostic tests on IVF embryos produced by 24 couples. These couples included one suffering from OCT, four with a predisposition to cystic fibrosis, two female carriers of Duchenne's disease, two couples carrying the spinal amyotrophia gene and two carrying Steinert's disease. Three hospitals in France are working on pre-implantation diagnostic testing and among them can screen for 30 different genetic diseases.