New embryo test for genetic diseases

A new embryo test has been developed which could help reduce the risk of couples at risk of serious genetic diseases of having an affected baby.

The test, which was developed by a team from Guy and St Thomas' NHS Trust in London, is being launched at a fertility conference in Prague on Monday.

It has already been used by the team for three months and they said that five couple were now expecting healthy babies following the test and IVF treatment.

The test is known as pre-implantation genetic halotyping (PGH) and scientists say that it will also improve reliability of diagnosis and increase the success rate.

The technique would be used to help couples receiving IVF treatment who are at risk of having a child with a serious genetic disorder, such as cystic fibrosis, sickle cell disease and spinal muscular atrophy, to select and embryo which will be unaffected.

A single cell is taken from each embryo and analysed to distinguish between the embryos which carry a genetic disorder and those which do not. One or two unaffected embryos are then transferred to the woman's womb in the hope that this will result in a pregnancy unaffected by the specific genetic condition.

Until now, clinicians had only been able to diagnose relatively common conditions and those where the gene mutation is the same for all those affected, because of the complexity of diagnosing genetic disorders in embryos.

However, the new technique will be able to diagnose conditions more accurately by first amplifying the DNA from the single cell they extracted from the embryo to replicate the cell's genetic material by a million times.

DNA finger printing is then used on the cells and this allows clinicians to distinguish between the chromosomes carrying the affected gene and those that do not. This means that the affected gene can be tracked without having to look at the actual mutation.

The team said that they had begun to use PGH for cystic fibrosis. For couples who are at risk of having a child with an X-linked disorder (where females carrying the disorder are not affected, but the 50% of males who carry it are), such as Duchenne and Becker muscular dystrophy, the technology will also increase the number of embryos that can be implanted.

Previously, tests could ensure that only unaffected female embryos were used. However, PGH would allow clinicians to identify unaffected male embryos as well as increasing the total number of embryos available and improving the chance of pregnancy.

Alison Lashwood, consultant nurse in genetics who worked with the team who developed PGH, said: "Pre-implantation genetic halotyping has revolutionised the service we can now offer. It puts together two technologies which have been used before, but it is the combination of these that has made the major difference.

"We are thrilled to have developed this technology as it opens up new possibilities to a number of couples who at risk of conceiving a child with a serious genetic disorder."

However, Josephine Quintavelle of Comment on Reproductive Ethics, said: "I am horrified to think of these people sitting in judgement on these embryos and saying who should live and who should die."

(KMcA/SP)