Carrier screening, or the genetic compatibility test, is a blood or saliva DNA test that is a study for future parents and allows us to detect whether they are carriers of a genetic disease or not 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 that 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 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 minimize 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.
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 have resulted in the introduction of the so-called expanded carrier screening, which essentially means offering to screen 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 Instituto Bernabeu, for example, we have an available program that can discriminate over 600 recessive genes.
In our opinion, this expanded carrier screening program could be a valid option over the standard ethnicity-based program, 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 program.
Since genetics has become a very important tool in reproductive medicine, we can offer patients 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, 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 be sure that we won’t have babies with a life-threatening disease or important disease that may give them a very bad quality of life. It is also an important test for couples going into IVF programs, 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 to select only the non-affected embryos.
