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PGD: Embryo Screening for Genetic Diseases

written by: •edited by: Paul Arnold•updated: 12/5/2009

Preimplantation genetic diagnosis (PGD) is a way of screening an embryo produced by IVF. It takes place before implantation to search for genetic mutations that could develop into a chronic disease. The aim is to select an embryo that is free of the disease it is being screened for.

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    What is PGD?

    This form of genetic screening is available for parents who conceive children by In Vitro Fertilization (IVF) and who have a family history of a particular genetic disorder. It involves taking a cell from a three day old embryo when it is at the eight cell stage. The cells are identical at this time as they have not differentiated, and the embryo is not damaged during the process.

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    Embryo Screening for Genetic Diseases

    The extracted cell then undergoes a serious of genetic tests to determine whether it has any chromosomal or genetic abnormalities. A procedure known as FISH (fluorescent in situ hybridisation) is employed to look for chromosome disorders and PCR (polymerase chain reaction) can detect mutations at the gene level.

    In theory this kind of embryo screening for genetic diseases can be used to look for any condition that is caused by a mutation in a single gene, provided that a test has been developed that can find that specific gene. Currently the technique can look for many diseases such as Sickle cell anaemia, Cystic fibrosis and sex-linked genetic disorders like Fragile X syndrome.

    In this way couples are able to see if the embryo would be likely to inherit the genetic mutation, and if so, they can elect not to go ahead with implantation. It avoids the dilemma of abortion at a later stage.

    It is important to stress that in some situations, if an embryo is seen to have a particular genetic mutation, the development of disease is not inevitable.

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    Embryo Screening and Cancer

    In January 2009 the first baby in the UK to screened for a genetic form of cancer was born. Preimplantation genetic diagnosis was undertaken on an embryo to look for a mutated form of BRCA1, a gene that can cause cancer. Her family has a long history of the disease and if she had possessed a mutated copy of the gene there would’ve been an 80% chance of her developing the cancer. The girl will be spared the pain and trauma that the condition can cause.

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    PGD Controversy

    There are some who view the technology as a slippery slope towards 'designer babies', a world where parents, in theory, could select the traits they want for their children. PGD can be used to determine the sex of a child, though it is illegal in most countries to use the technology in this way for social reasons. But it can be used to prevent selecting an embryo with a sex-linked genetic mutation. What about the selection of eye colour or intelligence? Many traits are the result of many genes and multigene/environment interactions. Even if the technology could screen for all traits it is unlikely that states would allow this to happen.

    There are also those who believe that PGD devalues the lives of disabled people, that embryo selection is a drive to create a population of 'perfect' people. Proponents of the technology counter that it is simply a way of preventing further generations from suffering from some of mankind's most dreadful diseases that have blighted previous generations. If we have the power to do that wouldn't it be immoral not to use it? It is a tough area and there are no easy answers, but now that we have these techniques available, governments and regulatory authorities must wisely consider how and when they are to be used.