FAQs - Preimplantation Genetic Diagnosis (PGD)

 

Q: What is preimplantation genetic diagnosis?

Preimplantation genetic diagnosis (PGD) involves genetically testing an embryo in a laboratory. In order to achieve this, couples have in vitro fertilisation (IVF) treatment followed by an additional genetic testing stage. The embryo is grown in the laboratory for a couple of days until the cells have divided and the embryo consists of eight cells. At this time a specially trained embryologist will remove one or two of the cells. The cells can then be tested to see if the embryo from which they were removed contains the faulty gene that causes the condition in the family. One or two of the embryos without a copy of the faulty gene can be placed into the woman in the hope that they will develop. Any remaining unaffected embryos can be stored for later use as required. Those embryos that had a copy of the faulty gene are allowed to perish.

More information on PGD can be found in the Guide to Infertility

 

Q: What other conditions can you test for using PGD?

The HFEA has licensed PGD for over 60 genetic conditions. The table below list examples of some conditions that have been licensed for PGD.

Examples of licensed PGD conditions (26.7 Kb).

 

Q: How do you decide what conditions to use PGD for?

When an application is received by the HFEA to do PGD the final decision about whether to licence the condition is made by a Licence Committee. In reaching its decision, the Licence Committee will consider whether the proposed treatment is lawful under the Act. Following this, they will satisfy themselves that the decision to provide treatment by the centre has been properly made having regard to the Guidance in the Code of Practice and the HFEA policy. See the Code of Practice.

 

Q: What is penetrance?

Penetrance refers to the likelihood of the condition manifesting in an individual if they carry a faulty copy of the gene. The higher the penetrance, the greater the chance of the condition developing in an individual with a faulty copy of the gene.

Most conditions licensed by the HFEA for PGD, are fully penetrant. This means that the condition will inevitably develop in individuals that carry a faulty copy of a gene.

For lower penetrance conditions, having a faulty copy of the gene increases the chance of developing the condition compared to the general population, but does not guarantee that the condition will develop.

 

Q: Can anyone have PGD to ensure that their child does not inherit the susceptibility gene that causes breast cancer?

It is only possible to do this test for people that know they carry a specific mutation that predisposes them to a type of cancer. Most cancers develop sporadically. It is thought that less than 10% of people that develop breast or bowel cancer do so because of an inherited fault. Unless there is a strong family history of breast cancer in your (or your partner's family), it is unlikely that your child will inherited a gene that increases the risk of developing cancer.  For more information you could talk to your GP.

 

Q: How do I know if I have an inherited susceptibility to cancer?

It is relatively rare for people to have an inherited susceptibility to cancer. Most people that develop cancer will not have the inherited form but instead will have developed a sporadic cancer. If there is a strong family history of a specific cancer or if you are concerned, you may wish to talk to your GP who will be able to advise you and if necessary refer you to a clinical genetics service.

There may be a genetic risk if:

  • Two or more close family members have been affected before the age of 50,
  • Three or more close family members have been affected before the age of 60,
  • Four close family members have been affected at any age.

If there is a genetic risk, it would be necessary to identify the specific change associated with the increased risk of cancer before PGD could be available. This may require genetic testing.

 

Q: Where can I get more information about inherited cancer conditions?

 

You can talk to your GP or practice nurse. Alternatively you may wish to look at the following websites:

General cancer information :
Rare genetic conditions:
Specific cancer organisations:

 

Q: What's different about the conditions discussed in Choices & boundaries?

The conditions that were considered in the Choices & Boundaries discussion are different to those previously licensed by the HFEA because they have a combination of features. The conditions in question have all of the following features:

  • they are later onset and
  • they are lower penetrance and
  • they are, in some cases, treatable.

The HFEA has licensed conditions that have one or other of these features. For example Huntington's is later onset and Retinoblastoma is not fully penetrant (although it does have a higher penetrance than inherited breast cancer).It is the fact that inherited breast and bowel cancer have a combination of all of these features that makes them different to others previously licensed by the HFEA.

 

It is expected that PGD will only be available where there is a significant risk of a serious genetic condition. The perception of the level of risk by those seeking treatment is an important factor in the decision making process. The seriousness of the condition is expected to be a matter for discussion between the people seeking treatment and the clinical team.

In any particular situation ? [the view of the people seeking treatment] ?are expected to be considered when deciding the appropriateness of PGD.

In any particular situation the following factors are expected to be considered when deciding the appropriateness of PGD:
(i) The view of the people seeking treatment of the condition to be avoided
(ii) Their previous reproductive experience
(iii) The likely degree of suffering associated with the condition
(iv) The availability of effective therapy, now and in the future
(v) The speed of degeneration in progressive disorders
(vi) The extent of any intellectual impairment
(vii) The extent of social support available and
(viii) The family circumstances of the people seeking
treatment

Last updated: 02 September 2008