At the fertility consultation we have different genetic testing to provide couples with complete genetic counseling. Depending on the family history, or the diseases that patients may have, different genetic tests can be done. One of them is the genetic study of carriers. This test identifies which autosomal recessive pathologies an individual carries.

What is a genetic carrier screening?

A genetic carrier screening aims to identify which autosomal recessive pathologies an individual carries. In the case of women, also identify X-linked diseases.

It is estimated that we all carry recessive diseases. However, in most cases, having a recessive pathology has no clinical consequences for the individual. That is why we do not know which pathologies we carry.

The likelihood of an individual carrying a recessive condition varies depending on the condition. In our population, some of the pathologies in which the frequency of carriers is highest are Cystic Fibrosis (1 in 36 people are carriers) or Spinal Muscular Atrophy (1 in 40 people are).

Autosomal recessive diseases

Autosomal recessive diseases are those in which the two copies of the gene (the copy inherited from the father and the one inherited from the mother) need to be altered to develop the disease. When only one copy of the gene is altered, the individual is a carrier of that condition.

A couple is at risk of transmitting an autosomal recessive pathology to their offspring when they are carriers of the same pathology. In this case, your child has a 25% risk of inheriting the disease, a 50% risk of being healthy as a parent and a 25% risk of being healthy and not a carrier.

   

X chromosome-related diseases

X-linked diseases are those in which the gene responsible is on the X chromosome. Women having two X chromosomes are carriers of the disease but men, being XY, develop the disease.

When a woman carries an X-linked disease, her daughters have a 50% risk of being carriers and their sons have a 50% risk of inheriting the disease. In some cases, women may present with clinical manifestations associated with the pathology. This is because one of the random X chromosomes is inactivated in each of the cells.

How is a genetic carrier screening performed?

It is made from DNA obtained from a peripheral blood sample. This sample sequences the genes associated with the recessive genetic diseases included in the study.

Who is it aimed at?

Carrier genetic screenings are an option for those couples who want to reduce the risk of their child developing a recessive disease.

• Knowing that both members of the couple have the same recessive pathology or that the woman has an X-linked disease, allows them to choose one of the available reproductive options to avoid transmitting the disease.
• In couples who will resort to a gamete donation, the study allows us to assign a donor who does not have the same recessive pathologies as the member of the couple who will contribute the gamete. If a donor has an X chromosome-related condition, it is excluded from the donation program.

Dra. Belen Garcia. Genetic counselor at FIVclínic.