Genetics - Genetic Testing
An introduction to genetic testing
Most babies born with 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 the child's confidence and self-esteem as they get older. We would not deny that having a child with 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.
To read the stories of some of our members' experiences of raising children with Ectodermal Dysplasia, please log-on to our membership area. Signing up to our membership area only takes a couple of minutes.
Before you decide whether or not it is appropriate for you or your child to undergo genetic testing, it is important for you to understand why you want this testing and how the results will affect you and 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.
Genetic tests are available for an increasing number of Ectodermal Dysplasia syndromes. Molecular diagnosis resulting from the analysis of a blood sample can confirm the suspected diagnosis of a condition in an individual and can ascertain whether the parents of an affected individual are carriers of the disorder and likely to pass the condition onto future children.
Molecular testing is not yet available for all the Ectodermal Dysplasia syndromes but is available for:
1) Hypohidrotic Ectodermal Dysplasia (HED) – both the X-linked form (XHED) and an autosomal form caused by mutations on chromosome 2q.
2) Clouston syndrome
3) Hay-Wells syndrome
4) EEC syndrome
5) Ellis-van Creveld syndrome
UK: Genetic testing under the National Heath Service can be a long process. It takes approximately 9 to 12 months for an initial blood sample to be analysed and a diagnosis made, and then a further 6 months to determine whether one or both parents are carriers. For more information about how to get blood tests analysed more quickly, please log-on to our membership area. Signing up to our membership area only takes a couple of minutes.
In an attempt to explain why such testing takes so long the following analogy may help. If you are asked to look for a word, such as 'testing' in a book containing say 500 pages this will take a very long time, however if you are asked to look on page 350 for the word 'testing' this narrows down the length of time; if you are then given a further clue such as page 350 second paragraph third line, you will find the word very quickly. Therefore finding the faulty gene in the first member of a family takes many months, once this gene has been found then the process is a lot quicker for the rest of the family.
The Ectodermal Dysplasia Society provides the following information to parents in order to help individuals to make an informed choice. The ED 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, that we just aim to support anyone trying to work out 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 Genetics Counsellor and with your doctor.
In vitro fertilisation (IVF) with pre-implantation genetic diagnosis (PGD)
Pre-implantation Genetic Diagnosis (PGD) is a means of detecting a specific genetic mutation within an embryo before it is transferred to the womb and forms a pregnancy. In order to undergo PGD, a couple must follow routine IVF treatment or perhaps ICSI (Intracytoplasmic Sperm Injection), especially if there are fertility issues too. ICSI is an in vitro fertilisation procedure in which a single sperm is injected directly into an egg.
When the embryos are 3 days old, one cell is removed from each for genetic testing (occasionally a second cell is required for confirmation). Healthy, unaffected embryos can be replaced 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.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is a very accurate antenatal test that detects chromosomal abnormalities such as Down's syndrome and genetic problems such as cystic fibrosis or muscular dystrophy. Testing for ED can also be carried out by CVS as long as the mutation present in the family is already known. The main advantage of CVS over amniocentesis is that it can be performed earlier – around the 11th week of pregnancy. You generally can't have an amniocentesis until the second trimester of pregnancy.
Many 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 disease such as Tay Sachs and they want to know as soon as possible whether this baby is affected. Many hospitals now offer CVS and it has become a popular alternative to amniocentesis.
For information on how the test is performed please log-on to our membership area. Signing up to our membership area only takes a couple of minutes.
Amniocentesis is the taking of amniotic fluid from around the fetus in the womb. Several diagnostic tests can then be carried out on that sample. It is used to detect possible chromosome abnormalities in the unborn child that may cause Down's syndrome or other congenital problems. It can also be used to detect genetic alterations causing other conditions, including ED, as with CVS.
Amniocentesis is performed from week 15 of the pregnancy onwards. Its main advantage over CVS is that it is somewhat less likely to lead the pregnancy to miscarry; its main disadvantage is that it takes place later in the pregnancy and often takes longer to produce a result.