The High Complexity Genetics Unit in fertility achieves high clinical gestation rates for healthy children

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    Genetics and its relationship with fertility

    It is estimated that 25% of women will suffer an abortion in their lifetimes. 50% of these miscarriages involve some type of chromosomal alteration. These abnormalities are often related to advanced maternal age.

    There are also many genetic diseases. It is estimated that 3-4% of births will suffer from such a disease. According to the Spanish Federation of Rare Diseases, there are between 5,000 and 7,000 rare diseases. 80% of these are of genetic origin and, therefore, susceptible to being transmitted to our children.

    Both scenarios pose a major challenge to assisted reproduction. Detecting these disorders early allows us to achieve high rates of healthy new-borns at home.

    High complexity reproductive genetics unit

    The Equipo Juana Crespo Genetic Unit provides personalised strategies for patients, offering a wide range of genetic studies according to their reproductive stage, family history and past pregnancy loss(es).  

    This unit’s primary goals are:

    • Personalised genetic counselling consultation. For each case, it is important to know the family genetic history and consider the best reproductive options to achieve a healthy pregnancy.
    • Proper advice on the appropriate tests to be performed at each stage.

    Genetic testing in pregnancy planning

    A test also known as a karyotype test for fertility, which is part of routine, basic fertility testing for men and women. A blood sample from the patient is used to examine a person’s chromosome set and report information about possible numerical (trisomies, monosomies, etc.) and structural (duplications, deletions, insertions, etc.) abnormalities that they may have. 

    If either parent is a carrier of an abnormality in their karyotype, this may be causing the formation of chromosomally abnormal embryos, which can lead to implantation failures, miscarriages or even diseases compatible with life.

    A cytogenetics technique performed on the semen sample to analyse the male gamete chromosomes. It is indicated in the male infertility study. One of the drawbacks of this test is that it analyses a sample that will not be useful. Therefore, it is an estimate and not a diagnosis as such.

    A test that minimises the transmission of recessive or X-linked genetic diseases to children. This test can identify mutations in the reproductive partner’s genes and detect whether or not there are matches.

    Carriers of mutations in any of these genes have a normal copy of the gene that is dominant over the mutated copy. Therefore, they have no symptoms. The risk appears when both members of the couple present mutations in the same gene. In this case, the probability of having an affected child is 25% for each pregnancy.

    It is indicated in the following cases:

    • For couples wishing to have children, irrespective of whether they have a history of genetic disorders in their family.
    • For couples with a blood relationship, as the probability of sharing mutations in the same gene is far higher.
    • For couples who go to assisted reproduction clinics and are going to undergo an in vitro fertilization process, both for treatment with their own gametes, and with donated gametes.

    After the study, the results of the genetic parents must be compared to determine the suitability or “genetic compatibility”.

    For gamete donation treatment, a donor negative for genes with mutations present in the recipient will be assigned.

    For couples with their own gametes, if there are matches in mutations in the same gene, they will be informed of the reproductive options to avoid transmission of the disease:

    • Preimplantational genetic test in embryos obtained through in vitro fertilization.
    • Change of gamete(s) in either parent.

    Genetic testing at the preimplantation stage of the embryo

    PGT or Preimplantation genetic testing. The study performed on embryos generated through in vitro fertilization techniques, which reveals whether they are affected by any chromosomal or genetic alteration before transfer to the mother’s uterus. This prevents the transfer of embryos that may cause serious diseases or that might not result in a healthy or full-term pregnancy.

    Depending on the study objective, the  types of PGT are:

    This study reveals if there is the correct number of chromosomes in the embryo’s cells. These structures contain all the genetic information (DNA). Each cell must contain 23 pairs of chromosomes, otherwise the embryo could result in implantation failure, miscarriage or even a chromosomal disease such as Down syndrome, which is due to trisomy, i.e. an extra copy of chromosome 21.

    PGT-A or of chromosomal alterations is indicated for:

    • Old maternal age. There is an exponential increase in abnormal embryos related to maternal age.
    • Repeated abortions. About 50% of miscarriages are due to chromosomal alterations.
    • Prior elective abortions due to chromosomal alterations.
    • Repeated implantation failures
    • Altered sperm FISH analysis
    • When one member of the couple has an altered karyotype structure. While it might not affect the parent, it can affect their children. In the latter case, the study is considered a subtype of PGT-A and is called PGT-SR or Structural Reorganization PGT.

    This study reveals whether the embryos are affected by a severe familial disease caused by variations (mutations) in a specific gene. Our DNA is made up of thousands of genes, each comprising a code that translates into a specific bodily function. If this code varies (is mutated), it can lead to disease.

    PGT-M is indicated:

    • In patients with a hereditary disease, in a partner or family member.
    • In patients with a matching compatibility test for the same disease in both members of the couple, to avoid transmitting it to their children.

    To perform this type of test on embryos, an Informativity Study must first be conducted. This study prior to PGT-M consists of genetic testing of the couple and their relatives to obtain further information about the disease and validate the diagnostic possibilities for future embryos.

    As its name indicates, a study that combines the two previous technologies.

    It is indicated when there is an indication for PGT-M and when any of the circumstances or indications for PGT-A are present.

    Prenatal or pregnancy stage Genetic Testing

    Equipo Juana Crespo believes it is important to know the reasons for early pregnancy loss. Therefore, we perform a genetic study of pregnancy remains and explore possible causes of miscarriage. In 50% of cases, the cause is chromosomal and can help us to direct subsequent treatment.

    Screening performed during pregnancy (from the 10th week of pregnancy onwards) that analyses foetal DNA circulating freely in the mother’s bloodstream.

    This is a non-invasive test enabling detection of the presence of chromosomal alterations (aneuploidies) without having to undergo an invasive test. In the event of an altered result, confirmation by amniocentesis is recommended.

    Non-invasive prenatal testing is primarily indicated for:

    • Old maternal age.
    • High-risk result in a biochemical or ultrasound screening.
    • History of pregnancy with chromosomal alterations.
    • Pregnant women of any age who have completed 10 weeks of pregnancy.
    • Pregnancies conceived naturally.
    • Pregnancies achieved through In Vitro Fertilization (IVF):
      • With own gametes.
      • With gamete donation.
    • Single or twin pregnancies.

    Frequently Asked Questions

    What results can I expect in my embryos after the PGT-M? How many embryos will be healthy?2023-01-03T13:13:21+01:00

    First, we must be aware that hereditary diseases are caused by a series of changes, also called mutations, in the genes making up our DNA. We have two copies of most genes, one inherited from our mother and the other from our father.

    The number of healthy embryos expected depends on the type of inheritance of these changes.

    If, for example, the disease has an autosomal dominant inheritance, 50% of the embryos generated are likely to be healthy and transferable. Only half of the children will inherit the mutation from the affected parent.

    However, if the disease is autosomal recessive, it will only manifest itself if both copies of the gene are affected, i.e., the mutation has been inherited from both parents. If this occurs, the probability of an affected child in each pregnancy is 25%. If only one parent has a disease-causing variant, their children will not be affected, and will have a 50% chance of being healthy carriers like their parent.

    There are also diseases with a particular type of inheritance. When the disease-causing variants are in the X chromosome, they are called X-linked. Females have two X chromosomes while males have only one. Males who inherit these variants are always affected, while females are often unaffected carriers.

    I have heard of PGT, TGP, PGD and PD. What is the right term?2023-01-03T13:07:27+01:00

    PGT and TGP refer to the same term, but in English and Spanish respectively. In English, PGT stands for Preimplantational Genetic Testing. As it’s the international scientific language, this is the most common. TGP in Spanish refers to the same test. PGD stands for Preimplantational Genetic Diagnosis and PD for Preimplantational Diagnosis. The latter two are increasingly uncommon, as this analysis is not considered a diagnosis as such, but instead screening of a representative part of the whole embryo.

    Why don’t my embryos undergo a PGT-A?2023-01-03T13:08:11+01:00

    It may seem like the PGT-A would guarantee success for all patients if a healthy embryo is transferred. However, this is not the case. If there is no clear indication, embryo biopsy is not recommended because, after all, it is an invasive technique. This technique has been proven to reduce implantation failures and miscarriages, but at EMC we prefer to personalise all treatments and techniques, including PGT.

    Does PGT-A study all diseases? Will my child be born 100% healthy?2023-01-03T13:08:48+01:00

    PGT-A does not study all existing diseases. It studies chromosomal alterations, some of which may give rise to diseases we are already aware of, such as Down syndrome, Edwards’ syndrome, Patau’s syndrome, etc. Although science is advancing rapidly and the panel of genes to be studied is becoming broader, there is currently no test that guarantees a completely healthy child with no diseases.

    What type of results can I get from a PGT-A?2023-01-03T13:09:32+01:00

    The following results can be obtained from a PGT-A study:

    • Normal embryo: All cells analysed have the correct number of chromosomes and are therefore suitable for transfer.
    • Abnormal embryo: The alteration of one or more chromosomes is observed in all the cells analysed. For example, an extra chromosome 18 (trisomy) is responsible for Edwards’ syndrome. This embryo is not suitable for transfer.
    • Potential mosaic embryo: Both altered and normal cells are observed in the set of cells analysed. Depending on the characteristics of the anomalies involved, a recommendation may be made regarding considering it for transfer. This should be discussed in a genetic counselling consultation with qualified personnel.
    What results can I expect from a PGT-A?2023-01-03T13:10:23+01:00

    Given maternal age is a determining factor in the number of normal embryos, it should be known that the older the patient, the lower the probability of getting a normal embryo to transfer.

    However, the probability of obtaining potential mosaic embryos is independent of maternal age. At EMC, our potential mosaic embryo rate is around 12%.

    If I take a PGT-A, do I no longer need Non-Invasive Prenatal Testing?2023-01-03T13:11:21+01:00

    Personalised counselling is recommended in each case to indicate non-invasive prenatal testing (NIPT). However, it is important to know that no modern genetic test is 100% diagnostic. Therefore, even if a PGT-A is performed, a NIPT may still be done later.

    Will I be able to see if my baby is healthy from hereditary diseases through Non-Invasive Prenatal Testing?2023-01-03T13:14:01+01:00

    Non-invasive prenatal testing does NOT study hereditary diseases. This testing only studies chromosomal alterations. If there is a suspicion of a pregnancy affected by a hereditary (monogenic) disease, invasive prenatal testing on an amniotic fluid sample (amniocentesis) is indicated.

    When transferring an embryo analysed via PGT-M, the recommendation is the same, but the probability of an altered result is considerably lower.

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