Carrier screening

It is a genetic study that makes it possible to determine whether a person is a carrier of a known mutation responsible for a specific disease. The fact that a person is a carrier of a mutation does not confer the risk of suffering from it, but it can cause serious problems in their offspring.

A carrier is a person who has a defective copy (a mutated allele) of a gene associated with a particular disorder. Humans have two copies of each gene (with the exception, in men, of some genes located on the X chromosome, which are not present on the Y chromosome), and in most cases, one copy in good condition is sufficient for the proper functioning of our organism. Carriers are usually unaware that they are carriers, as they have no symptoms or only mild symptoms.

Carrier testing can be done either before or during pregnancy. If testing is done before pregnancy, there is a wider range of options and more time to make decisions. For example, if a risk of severe genetic disease is identified, pre-implantation diagnosis can be considered. If the test is performed during pregnancy and a high risk of a serious genetic disease is identified, the couple still has a number of options.

Most carrier screening tests are for recessive disorders. This type of disorder only occurs if a person has inherited two defective copies (two mutated alleles) of a gene (one from the mother and one from the father).

In Europe, the most common autosomal recessive disease is cystic fibrosis. The disease causes destruction of the lung structure and reduced physical resilience due to inflammation of the airways. The prognosis for those affected has improved considerably due to medical advances, including lung transplantation.

Spinal muscular atrophy is another common autosomal recessive disease. It is characterised by progressive degeneration of nerve cells in the spinal cord. Despite advances in treatment, the prognosis for many patients remains poor.

An X-linked recessive disease is a disease that is inherited through the X chromosome. Since males only have one X chromosome (their other sex chromosome is the Y chromosome), if they inherit the defective copy from their mother, they only have that copy and manifest the recessive disease.
If the mother is a carrier, there is a 25% risk that she will have a male child with the disease. At the same time, 50% of the offspring (boys and girls) are healthy and are not carriers. 25% of the offspring are healthy girls who are carriers like the mother or are mildly affected (e.g. in Fragile X syndrome).
Situations where both members are carriers do not usually occur, as in the case of boys they would manifest the disease.

The various autosomal recessive diseases cause a wide variety of clinical pictures with a wide variety of prognoses.

• Some are not compatible with normal embryonic development (survival) and result in the death of the foetus already during pregnancy (miscarriage).
• Other diseases can lead to severe congenital, mental or physical disability.
• In some cases, life expectancy and quality of life are practically unaffected if therapeutic measures are taken in time; for other diseases, there are no treatment options.

In certain circumstances, the risk of developing a disease may be detected at a later stage of life, which does not affect life expectancy, but for which there are nevertheless no or very limited treatment options.

Consequently, the considerations and consequences for couples in case of an abnormal test result vary.

To determine whether either partner is a carrier of a disease-associated mutation, a blood or saliva sample is required. This test will be analysed using molecular techniques to determine whether either partner is a carrier of a recessive disease-associated mutation.

If a predisposition for the same autosomal recessive disease is found in both partners, this means a risk of 25% per pregnancy for the occurrence of this disease. The options depend on the timing of the test, the individual decision of the couple and the legal possibilities in the country.

• If the test is performed before pregnancy and the possibility of a serious genetic disease is detected: Preimplantation diagnosis is possible. In this case, the embryo is examined at an early cellular stage within the framework of in vitro fertilisation to determine whether the mutation is present in both copies of the gene. Only unaffected embryos are used. It is limited to severe diseases and must be approved in advance by an ethics committee in Spain.
• If the test is performed during pregnancy: The genetic material of the foetus is examined by prenatal testing for the presence of the disease.

You can contact us and we will inform you about the costs of carrier analysis.

As a general rule, genetic counselling is not covered by any type of health insurance.

Genetic tests are covered by some private insurance companies and sometimes depend on certain criteria (patient’s medical history, family history, abnormal findings in ultrasound scans, etc.). You can come to us with a certificate from your doctor or with your insurance card.