Testing For Hereditary Diseases: Genetic Compatibility Test (GCT)

By (gynecologist), (embryologist), (gynecologist), (gynecologist), (embryologist) and (biochemist).
Last Update: 10/06/2022

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.

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.

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.

GCT is capable of analyzing about 550 genes, in which it can detect up to 4,500 mutations linked to more than 600 recessive genetic diseases.

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.

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?

By Inmaculada Díez M. D. (gynecologist).

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?

By María Ortega Ortega B.Sc., M.Sc. (embryologist).

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?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

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?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

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?

By Pascual Sánchez Martín M.D., M.Sc. (gynecologist).

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?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

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?

By Paloma Sánchez Gómez M. D. (gynecologist).

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.

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?

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Hane Htut Maung. Ethical problems with ethnic matching in gamete donation. J Med Ethics. 2019 Feb;45(2):112-116. doi: 10.1136/medethics-2018-104894. Epub 2018 Dec 8 (view)

Ilan Tur-Kaspa, Roohi Jeelani. Clinical guidelines for IVF with PGD for HLA matching. Reprod Biomed Online. 2015 Feb;30(2):115-9. doi: 10.1016/j.rbmo.2014.10.007. Epub 2014 Oct 18 (view)

Molly R Payne, Anne-Bine Skytte, Joyce C Harper. The use of expanded carrier screening of gamete donors. Hum Reprod. 2021 Apr 11;deab067. doi: 10.1093/humrep/deab067. Online ahead of print (view)

FAQs from users: 'When should GCT be performed?', 'What is the solution when there is infertility due to genetic incompatibility?', 'What if I find out I'm a carrier of a genetic mutation?', 'How important is the genetic compatibility test?', 'What can I do if I am genetically incompatible with my partner?', 'How much does the genetic compatibility test cost?' and 'Does it make sense to do genetic matching after PGD on embryos?'.

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Authors and contributors

 Inmaculada Díez
Inmaculada Díez
M. D.
Inmaculada Díez is the head of the Assisted Reproduction Unit at Ginemed Jerez. Inmaculada studied Medicine at the University of Seville. More information about Inmaculada Díez
Member Number: 411108291
 María  Ortega Ortega
María Ortega Ortega
B.Sc., M.Sc.
Degree in Biology and Biochemistry from the University of Salamanca. She has a Master's Degree in Human Reproduction from the Complutense University of Madrid and another one in Nutrition and Health from the Open University of Catalonia. More information about María Ortega Ortega
Licence number: CLM-0180
 Pascual Sánchez Martín
Pascual Sánchez Martín
M.D., M.Sc.
Dr. Pascual Sánchez Martín has a degree in Medicine from the University of Salamanca and specialized in Obstetrics and Gynecology at the Virgen del Rocío University Hospital. More information about Pascual Sánchez Martín
Licence number: 414110807
 Valeria Sotelo
Valeria Sotelo
M.D., M.Sc.
Bachelor's Degree in Medicine from the University of Buenos Aires. Specialist in Gynecology & Obstetrics. Master's Degree in Video-laparoscopic Surgery, and Certificate of Specialist in Gynecology. Associate Member of the Spanish Fertility Society (SEF) and the Spanish Society of Gynecology & Obstetrics. More than 10 years of experience in the field of Reproductive Medicine. More information about Valeria Sotelo
License: 030309166
 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Michelle Lorraine Embleton
Michelle Lorraine Embleton
B.Sc. Ph.D.
PhD in Biochemistry, University of Bristol, UK, specialising in DNA : protein intereactions. BSc honours degree in Molecular Biology, Univerisity of Bristol. Translation and editing of scientific and medical literature.
More information about Michelle Lorraine Embleton

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