Is carrier screening and matching for donor/recipient recommended by doctors?
The term carrier screening is not familiar to many patients; genetics, however, are a major part or reproductive science. All of us carry genetic mutations; some of us may be carriers of genetic diseases we could pass on to our children. Carrier screening is exactly what it says on the tin: it’s a test which can determine if a patient is a carrier of a genetic disease that could impact their children. How exactly is this test conducted? What diseases can it detect? Should I undergo testing? Is it worth doing in donation scenarios?
To answer these questions – and more – we asked three IVF specialists to tell us all about carrier screening.
Our experts are:
- Dr. Maria Arque, Fertty International, Spain
- Dr. Juan Carlos Castillo, Instituto Bernabeu, Spain
- Dr. Laura de la Fuente Bitaine, Clinica Tambre, Spain
Answer from Dr Arque
Carrier screening, or the genetic compatibility test, is a blood or saliva DNA test that is a study for the future parents and allows us to detect whether or not they are carriers of a genetic disease that they could pass onto their children. According to our experience, one out of every two patients who undergo this test are carriers of genetic diseases without even knowing it, which means that even though they are carriers, they are not going to be affected by or develop this disease. If both members of the couple, or the egg donor and the husband whose sperm is going to be used are carriers of the same disease, there will be a 25% risk of the baby having this disease. These genetic compatibility tests usually allow us to detect this situation where this could occur by identifying a lot of genetic diseases which would have a very poor prognosis in the children, or have a very detrimental effect on the quality of life of the child that is born with it. Some examples are cystic fibrosis, Fragile X syndrome or spinal muscular atrophy, among other diseases. This test is a preventative measure that is performed before starting the fertility treatment, and in order to determine whether the future father or the egg donor are carriers of this disease, and in that way we can select an egg donor that, in the case where the husband is a carrier of a specific genetic disease, is not a carrier of this disease, to minimise that risk. Not all genetic diseases are preventable by these tests, as the tests have some limitations and do not test for all genetic diseases possible, but it is a very good way to reduce the risk of the diseases happening.
Answer from Dr. Castillo
Carrier screening refers to the process of identifying individuals looking for pregnancy who would be at risk of transmitting recessive hereditary traces to their offspring. The vast majority are patients with no family history of disorders unless consanguineous and because the vast majority of these conditions are asymptomatic, the carriers will never be aware of their status unless screening is performed. Historically, carrier screening has been offered for selected conditions to specific populations from particular ethnic backgrounds and this is still the most popular approach in almost every fertility centre. In Spain, for example, the board of the Spanish Fertility Society recommends screening for this condition called cystic fibrosis, which is the most common genetic condition in the Mediterranean area, before proceeding with any gamete donation and, additionally, to rule out the condition called Fragile X Syndrome in egg donors. More recently, advances in technology and cost savings has resulted in the introduction of the so-called expanded carrier screening, which essentially means offering screening to all patients regardless of their ethnic background. This approach encompasses genetic analysis in a growing number of genes for an increasing number of rare conditions. At the Intituto Bernabeu, for example, we have available programme which is able to discriminate over 600 recessive genes.
In our opinion, this expanded carrier screening programme could be a valid option over the standard ethnicity-based programme, especially for patients seeking additional information before pursuing conception. The main advantage is that these patients will have the option of doing a pre-implantation genetic diagnosis within the embryo in the case of being carriers of these recessive traits. Before proceeding with the expanded carrier screening, of course it’s mandatory to give the patient full information about the pros and cons, benefits and limitations of the technique as well as the interpretation of the results. We consider this as crucial before embarking on the expanded carrier screening programme.
Answer from Dr. Bitaine
Since genetics has become a very important tool in reproductive medicine, we can offer patients a whole screening of many mutations in their chromosomes. We are all carriers of genetic mutations and these mutations won’t cause us any problems, but they may cause problems in our babies. That means that we may be carriers of some abnormalities or mutations that, when combined with mutations of our partner, can cause our baby to be born with abnormalities. These are what we call recessive diseases, and these will only appear when both of the parents are carriers of these mutations. Since we know these are possible to detect with a simple blood test, we have started to do these tests in IVF clinics. We do them especially when we are searching for donors, be it egg donors or sperm donors, to make sure they don’t have the same mutations as present in the future parents. So, this is a very important tool to have more security and to be sure that we won’t have babies with life threatening disease or an important disease which may give them a very bad quality of life. It is also an important test for couples going into IVF programmes, so we can check that the baby is not affected by one of these diseases, and we can even do genetic diagnostic tests in the embryos, in order to select only the non-affected embryos.