Ehlers-Danlos syndrome (EDS) is a genetic condition, which means it is caused by a mistake (a mutation) in one of our genes. In most types of EDS, this mutation has been identified, and genetic testing can be done to find this mutation and confirm the diagnosis. You will only be referred for testing if it is felt by a geneticist that your symptoms are suggestive of one of the rare types of EDS.
Unfortunately, in the most common type of EDS, the hypermobility type, a gene mutation has not yet been identified and so it cannot be tested for. In classical EDS, a mutation has been found but it is only present in 50% of people with the condition. This means that it is possible to be diagnosed with classical EDS even after a negative genetic test. There are currently several research projects underway attempting to identify the genes responsible for these types of EDS.
For the other main types of EDS – Vascular, Kyphoscoliotic, Arthrochalasia, Dermatosparaxis and some cases of Classical – the gene has been identified and can be tested for to confirm a diagnosis. Several types of embryo screening are also available and will be described later.
If you are referred for genetic testing you will most likely be seen by either a Clinical Geneticist or a Genetic Counsellor. They will be able to discuss your condition with you and explain the test that you are being offered and the possible outcomes. Genetic testing is usually done with a blood sample, although in some cases they may use a saliva sample or a skin biopsy for testing. When your sample is sent off, the laboratory will extract your DNA from the sample.
DNA contains the instructions of how to make everything in your body. A copy of your unique DNA is found in almost every cell of your body. Once the laboratory has extracted the DNA from your sample, they will sequence your DNA, which is like reading the instructions. This takes a long time as there are over 20,000 genes in your body. Once the DNA has been sequenced, it will be analysed by comparing it to a sequence of ‘normal’ DNA to see if your DNA has any mutations in the genes that may be causing the EDS.
In genetic testing, they will not look at all of your DNA but only at the genes that cause EDS so that they can look for a mistake in those genes. These are genes that make collagen and other components of the connective tissue. When there is a mistake in the gene, the connective tissue made in your body is faulty, which results in EDS. The laboratory will send the result of the test back to your geneticist who will pass the results on to you. This testing can take up to several months as there is a huge amount of time and work involved in the testing.
This genetic testing can confirm a clinical diagnosis and the type of EDS you have. It is also useful to find out what mutations you could potentially pass on to your children, and may also help other members of your family get a diagnosis.
Another type of genetic testing is embryonic testing. There are two types of this: Pre-implantation Genetic Diagnosis (PGD) and pre-natal testing in utero. PGD is only approved for use in the Vascular and Classical types. Pre-natal testing in utero can be used for these as well as the Kyphoscoliotic, Dermatosparaxis, and Arthrochalasia types, although the tests available may differ depending on centre. The mutation must have already been found in the affected parent so that the laboratory can look for this specific mutation in the embryo.
PGD is a relatively new technology which can be used to make sure that your child is not affected by the condition. The conditions which can be treated in this way are governed by the Human Fertilisation and Embryology Authority (HFEA) as there are a lot of ethical concerns to be addressed in PGD. There is a list of all of the conditions approved by the HFEA on their website. This will not be the right decision for all couples and it is important that you discuss this option fully with your geneticist, including the risks involved, before you make a decision. Some people are against the technology for ethical, moral, or religious reasons. It also carries some risks for the woman undertaking the treatment, and in a few cases it can be very dangerous.
PGD involves harvesting some eggs from the mother and sperm from the father and combining them in a laboratory. This is the same way that embryos are created in in-vitro fertilisation (IVF) therapy. Once the eggs have been fertilised and left to grow for a few days, a single cell is taken from each embryo and the genes are tested to see if the genetic mutation identified in the parent is present in the embryo. An embryo without the mutation is then implanted into the mother’s uterus. If there are further embryos without the mutation they are often frozen at this stage so they can be used at a later date if necessary. PGD therefore ensures that the child does not have the mutation that causes EDS and stops it being passed on to subsequent generations.
It is also possible to test a foetus in utero early in a pregnancy. Again it is necessary that the mutation has been identified in the parent so that this specific mutation can be looked for in the foetus. This involves taking a sample of either the placenta or some of the amniotic fluid. Cells can then be extracted from the sample and tested to discover if the foetus carries the mutation. Doctors will generally only test for this condition if the course of the pregnancy may be altered as a result; for example, if it is found that the foetus carries the mutation the parents may choose to abort the pregnancy. As the testing carries a small risk of miscarriage, it will not usually be not be carried out if the parents feel it would not change the course of the pregnancy. Again this is a very personal decision and should be discussed with your geneticist before going ahead with the testing.