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Genetics Testing

Prenatal testing

The ED Society provides the following information to parents to help individuals make an informed choice. The Society takes no position as to whether prenatal testing is “the right thing” for any individual or family; these questions are so personal, and can be so difficult, the Society just aims to support anyone trying to decide what it is best for them to do in their unique circumstances. The decision whether to undertake prenatal testing (during a pregnancy), or carrier testing (either before or during pregnancy), together with the risks and implications of such testing, should be discussed in detail with a Genetic Counsellor and with your doctor.

Chorionic Villus Sampling (CVS)

CVS is a very accurate antenatal test that detects chromosomal abnormalities such as Down’s syndrome and genetic disorders where the exact genetic alteration is known. Testing for Ectodermal Dysplasia can be carried out by CVS if the genetic alteration present in the family is already known for the couple with a significant chance of having a child affected by Ectodermal Dysplasia. The earliest a CVS test can be performed is from around 11 weeks of pregnancy. It is usually performed under local anaesthetic and involves the removal of a small amount of the baby’s placenta. The placenta contains the baby’s DNA and so placental DNA can be tested to see which genes the baby has inherited. This gives a couple the option of terminating a baby who may have inherited a severe form of Ectodermal Dysplasia. However, as the CVS involves inserting a needle into the womb there is a small increased chance of miscarriage as a result of having the test (around 1%).

Some women over the age of 35 choose CVS because the risk of having a child with a serious chromosomal abnormality increases significantly as you get older. Some women choose CVS because they already have a child with a birth defect, or they have a family history of a genetic disorder, but others decide against it because of the risk of miscarriage.

Amniocentesis

An alternative test is an amniocentesis (also referred to as amniotic fluid test or AFT). It is similar to a CVS, but in an amniocentesis a small amount of amniotic fluid containing foetal cells, is sampled from the amniotic sac surrounding the foetus. The foetal DNA can then be examined to see which genes the baby has inherited. This can be carried out from 15 or 16 weeks into a pregnancy. Again, as this is an invasive test there is a small increase in the risk of miscarriage as a result of having the test.

In Vitro Fertilisation (IVF) with Pre-implantation Genetic Diagnosis (PGD)

Pre-implantation Genetic Diagnosis (PGD) can be applied to embryos conceived in the laboratory (by IVF). PGD is a means of detecting a specific genetic alteration within the embryo before it is transferred to the womb to form a pregnancy. A specific license is needed for each genetic type of Ectodermal Dysplasia. X-linked Hypohidrotic Ectodermal Dysplasia is one of the licensed conditions. In order to undergo PGD, a couple must follow routine IVF treatment or perhaps ICSI (Intracytoplasmic Sperm Injection), especially if there are also fertility issues. ICSI is an in vitro fertilisation procedure in which a single sperm is injected directly into an egg. If the couple are not infertile, they have to use barrier contraception at the same time as having IVF treatment, to make sure conception does not occur “the usual way”.

When the embryos are 3 days old, one cell is removed from each embryo for genetic testing (occasionally a second cell is required for confirmation). Healthy, unaffected embryos can be placed in the womb when they are 5 or 6 days old. The success rates of IVF with PGD are similar to the success rates of normal IVF and depend, to a large extent, on the clinic where the IVF with PGD is undertaken. (Note that clinics often report their success rates in somewhat different ways, so it can be difficult to compare their “rates of success”). NHS funding for PGD is not guaranteed and depends on a couple’s individual circumstances (including their postcode).

Non-Invasive Prenatal Diagnosis (NIPD) or Testing (NIPT)

NIPD can be carried out for sex determination and is called ‘non-invasive’ because it is carried out on a sample of blood from the mother. The main advantages of NIPD are that it can be carried out earlier in pregnancy than current tests and that the procedure does not carry any risk of miscarriage. The test only requires a sample of maternal blood, rather than having to take a sample directly from the pregnancy as in other types of prenatal diagnosis, such as chorionic villus sampling (CVS) or amniocentesis. However, at present, this test can tell only whether the baby is a boy or a girl and does not detect which genes the baby has inherited.

In principle, this technology could also be used to identify an affected foetus early in a pregnancy. It is hoped that this will become possible within the NHS over the next couple of years. This may become very useful once foetal treatments (given in utero) have been developed and introduced (but these are not yet available as established treatments).