Testing For Hereditary Diseases: Genetic Compatibility Test (GCT)

The genetic compatibility test (GCT) is a test that minimizes the transmission of genetic diseases to children, since it is allows identification of altered genes in each member of the couple and detect if there is any mutation in common.

Concretely, GCT can prevent the transmission of some 600 genetic diseases, which do not have a definitive cure at present.

For this reason, it is interesting to know a priori the possible mutations that go unnoticed in the person and, in the case the couple share the same mutation, to know what actions to take at the moment of considering a pregnancy.

What is a recessive genetic disease?

A recessive inherited genetic disease is one in which both copies of the causative gene must be altered for the disease to manifest.

An affected person will have inherited 2 copies of the defective gene. one from the mother and another from the father. In contrast, the parents can be healthy carriers of the pathology, with only one copy of the defective gene, and have no symptoms or effects.

It should be noted that a large part of the population carries genetic mutations, which can be passed from generation to generation without being aware of it. Only if you connect with another person with the same mutation and have a child together, does the disease come to light.

Inheritance of a recessive genetic disease

The chance that a child will inherit a recessive genetic disease if both parents have a common mutation is 25%. On the other hand, the probability of only being a carrier of the disease will be 50% and, if totally healthy, 25%.

You can learn more about the inheritance of genetic diseases in detail in the following article: What are monogenic diseases?

Genetic compatibility test

Today, genetic diseases do not have a definitive cure. However, they can be prevented by a genetic compatibility test, also called carrier study or genetic matching.

Gynecologist Valeria Sotelo comments that:

About 7,000 genetic diseases are known today, and 1 in every 100 births may suffer from one of these diseases.

In the next section, we are going to comment on some interesting aspects of the GCT.

Indications for GCT

In general, any couple can have a genetic match test to find out what mutations are present in their genetic material, even if there is no family history of any pathology.

As we have said before, about 7,000 genetic diseases are known today, of which 56% of the population is a carrier.

However, it is most common to do a carrier study in the following situations:

Before an assisted reproductive treatment

more and more fertility clinics are recommending this study in order to better determine the most appropriate treatment. In addition, it is important to do so in couples with a history of a genetic disease or if one of them already knows it is a carrier.

Before treatment with gamete donation

GCT allows a better selection of the sperm donor or egg donor, so that they do not share the same mutations with the recipients. Today, most clinics guarantee the performance of GCT to all their candidates for gamete donation.

Consanguineous Couples

GCT is highly recommended when couples are related in some way, especially in "closed" ethnic groups or isolated geographic areas.

Indications of genetic compatibility test

How is the GCT performed?

As we have already mentioned, genetic compatibility analysis consists of determining a person's altered genes and analyzing them together with those of their partner to study the probability that their child will inherit a serious genetic disease.

In order to do this, it is simply necessary to draw blood from each of the parents and analyze the DNA using different genetic techniques.

The results of this genetic compatibility study usually take about 30 days, although this depends on the techniques used in the laboratory. Some clinics claim to have the results in 2 or 3 weeks at the most.

The most common monogenic recessive diseases in the population are cystic fibrosis, spinal muscular atrophy, hemophilia, fragile X syndrome, thalassemias and so on.

Thanks to the genetic compatibility test, it is possible to reduce the risk of having a baby affected by one of these diseases from 1% to less than 0.01%.

Prevention of inherited diseases

If the GCT results show that there is no common genetic mutation in both partners, they can seek pregnancy with the peace of mind that their children will not inherit the recessive diseases included in the study.

If, however, the same mutation responsible for some genetic pathology is detected in both parents, the risk of having a baby affected by this disease is 25%.

In this case, it will be necessary to take all necessary measures to avoid transmitting the hereditary disease to the children. The most common are the following:

Preimplantation genetic diagnosis (PGD)

although a couple does not have infertility problems, the presence of a recessive mutation in both parents is an indication for in vitro fertilization (IVF) with PGD. With this test performed on embryos, it is possible to select only those that are genetically healthy to transfer them to the mother's womb and discard the rest.

Gamete donation

is another possible option to avoid transmitting a genetic disease, bet it sperm donation or egg donation. Generally, gamete donors are also subjected to this genetic test, so we will study their compatibility with that of carrier patients.

How can we prevent recessive genetic diseases

In short, the genetic compatibility test is very useful to avoid or prevent the emergence of numerous recessive diseases that today have no cure.

Costs of GCT

The price of genetic testing varies from clinic to clinic and depends also on the complexity and nature of the test. This means that the costs increase if more than one test has to be performed or if other family members have to be screened as well.

In the U.S.

Genetic compatibility test ranges from $100 to $3,000 or higher. The majority of health insurance companies cover the costs of genetic counseling and genetic tests which is why patients are required to contribute with a small amount only or with no out-of-pocket costs at all.

However, insurance coverage is subject to certain requirements such as genetic predisposition.

In the U.K.

On the NHS, it is possible for patients to get genetic testing for free. For this reason, they need to be referred for it by a specialist. This is the case when the patient suffers from genetic diseases.

FAQs from users

When should GCT be performed?

As long as the couple wants it, it is always indicated. Normally, it is recommended in donors because they are someone who is already tested and then it is offered to the couple. But we have had couples come to us who have decided to have it done to avoid some type of recessive disease that they do not know about in the family.

What is the solution when there is infertility due to genetic incompatibility?

Genetic compatibility is determined by testing for carriers of recessive genetic diseases. Almost all of us are carriers of recessive genetic diseases, although some of them have no clinical relevance described at present.

Carriers of these recessive genetic diseases do not manifest any symptoms as they do not develop the disease, as for the disease to develop both partners must be carriers of the same gene. Even so, these couples will have a 25% chance of having a sick child, a 25% chance of the child being healthy and a 50% chance of the children being carriers of the same gene.

This genetic compatibility test is recommended in cases of egg donation. If the donor is tested for carriers, it is recommended that the recipient couple is also tested, to rule out the possibility that the egg and sperm are carriers of the same disease. In addition, in treatments with double donation, it is also advisable to carry out genetic matching between the donors before the treatment is carried out.

In cases where both members of the couple are carriers of the same disease and wish to use their own gametes, it is advisable to carry out a Preimplantation Genetic Diagnosis (PGD) treatment to select the embryos free of the disease.

What if I find out I'm a carrier of a genetic mutation?

Presenting a recessive genetic mutation does not pose any health risk and the disease will not develop. We are all carriers of numerous recessive genetic mutations. However, this type of mutation can go unnoticed for generations, unless two people carrying the same mutation are paired and a sick baby is born as a result of this union.

How important is the genetic compatibility test?

The main advantage of the genetic compatibility test is that it prevents the birth of sick children. For this reason, it is very important to detect which couples are carriers of a specific mutation that can be inherited by their offspring.

What can I do if I am genetically incompatible with my partner?

We call genetic incompatibilities those cases where we are carriers of a disease that requires the two genes we give to the embryo be affected for the disease to manifest.

If we have the disease in only one gene, the other one can do the job and the embryo will be normal. In this situation the parents will not present the disease, but may produce embryos that are affected by a disease. This is what we call genetic incompatibility.

If both parents have a mutation in one of the genes of a disease and if they both pass the mutation to the child, the child will not have a healthy gene and will have the disease. So those parents are genetically incompatible because they can have sick children.

In such cases we do tests to see if there is any type of incompatibility. We offer the couple embryo testing in the laboratory to find out if the embryos that we have generated have inherited two affected genes and therefore will be sick. If so, we will not use them. The embryos can inherit one correct gene and one mutated gene and be carriers like their parents, but healthy, and these embryos can be used. If two correct genes are inhereited a healthy embryo is the result and that we will obviously use.

How much does the genetic compatibility test cost?

The genetic compatibility test may range from $100 up to $2000, depending on each type and complexity of the test and whether more than one test is necessary.

When a test is recommended by your doctor, your health care provider may take over the costs of the GCT.

Does it make sense to do genetic matching after PGD on embryos?

It is not ideal. It would be advisable to do it before any assisted reproduction technique. It is true that if you are carriers of the same disease, then when doing the biopsy of the embryos we can see the ones that are not altered.

Recommended reading

PGD is the most important diagnostic test for preventing the transmission of a genetic disease to descendants. If you want to know all the details about this, you can read more here: What Is PGD or Preimplantation Genetic Diagnosis?

If you are already pregnant and want to know if the baby you are expecting is totally healthy, the indicated prenatal test is amniocentesis. You can find out what the following link consists of: What is amniocentesis?