Q&A: Preimplantation genetic diagnosis

Unaffected embryo can be implanted into the mother's womb

The Human Fertilisation and Embryology Authority has said it will allow doctors to screen IVF embryos for genes linked to cancer.

What is preimplantation genetic diagnosis?

Preimplantation genetic diagnosis, or PGD, was first introduced in 1990 as an experimental procedure.

It involves removing a cell from an embryo at the eight-cell stage of development, when it is around three-days old, and testing it for genetic disorders so that an unaffected embryo can be implanted into the mother's womb.

What were the rules on PGD?

PGD has traditionally been used to check for genes which will guarantee the resulting child will develop a condition - such as cystic fibrosis and Huntington's disease.

The HFEA has also allowed PGD can be used to check for an inherited form of bowel cancer called familial adenomatous polyposis and retinoblastoma - a very rare form of eye cancer.

It also gave the go-ahead for the technique to be used so that embryos could be selected purely because they are a tissue match for a sick sibling.

What has the HFEA decided this week?

It has approved the use of PGD to check for the BRCA1 and BRCA2 genes, which increase the risk of breast cancer by 80%. BRCA1 also increaes ovarian cancer by 40%.

Carriers of the HNPCC gene have about an 80% risk of colon cancer.

But having these genes does not mean someone will definitely develop the conditions - it only means a person will be susceptible to them.

And, unlike the conditions for which PGD is now used, people would not be affected until they were in their 30s or 40s.

What are the concerns about PGD?

There are concerns that medicine is moving away from treating diseases and focusing on eliminating the carrier.

Some argue that it might be possible to cure these genetic diseases in the future.

The extension to screening for "susceptibility" genes has also caused concern from disability campaigners, who fear pre-natal selection.