An introduction to genetic testing

Most of the babies born who are affected by an Ectodermal Dysplasia syndrome go on to lead full and happy lives even if they might need some extra love and care when they are younger. In addition, their parents, teachers and other adults in their environment will need to be aware of the condition and how it affects the child to help build their confidence and self-esteem as they get older. We would not deny that having a child affected by an Ectodermal Dysplasia syndrome can be a source of anxiety, but it should never be forgotten that such a child can also be a tremendous source of joy.

Genetic testing is available for some forms of Ectodermal Dysplasia, but this may not be relevant or appropriate for your family. The Ectodermal Dysplasia Society strongly advises individuals who are considering genetic testing to seek genetic counselling. A Genetic Counsellor can provide individuals and families with information on the medical management of a condition and the way in which a specific condition is inherited. They can also help you think about how genetic testing might impact on your feelings, and in that way help you decide whether genetic testing would actually be helpful for you at any particular time.

Some forms of the Ectodermal Dysplasias are diagnosed clinically, this means that Doctors will talk through the history of your symptoms, examine you and may then be able to match your pattern of problems to a specific Ectodermal Dysplasia syndrome.  Sometimes a clinical diagnosis is very difficult and unclear making an accurate diagnosis not always possible. The Doctor may suggest taking a blood sample for genetic testing.

Genetic tests are available for an increasing number of the Ectodermal Dysplasia syndromes. Molecular diagnosis resulting from the analysis of a blood sample can confirm the suspected diagnosis of an Ectodermal Dysplasia in an individual.  The same test can be carried out on the parents of an affected child to ascertain whether they are carriers of the condition and the likelihood of passing the condition onto future children.

Molecular testing is not yet available for all the Ectodermal Dysplasia syndromes.

In the UK Genetic testing under the National Health Service has often been a slow process and, in the past, testing has often been carried out in research laboratories. However, this is changing as new techniques of DNA sequencing enter the diagnostic laboratories.

The first step in arranging genetic testing in a family is often to identify the gene change responsible for the Ectodermal Dysplasia in one affected member. In the past, this has often taken many months as the laboratory may have needed to examine several genes. However, this process is now usually a lot faster as long as the clinical condition has been diagnosed with confidence, but the testing can still take 4-6 months to complete. Once the gene change has been found in one person, it is much simpler, quicker and cheaper to test any of their relatives as the laboratory then know exactly which gene to look at.

What happens at a genetics appointment?

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Prenatal Testing

The ED Society take no position as to whether or not 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 Society are able to provide some information to assist you in making an informed decision. However, 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

Chorionic Villus Sampling (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 affected by 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 the baby’s cells, is sampled from the amniotic sac surrounding the baby. The baby’s 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 with Pre-implantation Genetic Diagnosis

Pre-implantation Genetic Diagnosis (PGD) can be applied to embryos conceived in the laboratory by In Vitro Fertilisation (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 Intracytoplasmic Sperm Injection (ICSI), 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 must 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 woman’s age and also 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 whether or not they already have unaffected children).

Non-Invasive Prenatal Diagnosis or Testing

Non-Invasive Prenatal Diagnosis (NIPD) or Testing (NIPT) 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 or amniocentesis. However, at present, this test can only tell 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 fetus 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 fetal treatments (given in utero) have been developed and introduced (but these are not yet of proven efficacy).