Today, genetic diseases can be identified during pregnancy or after birth. However, possible genetic diseases in the baby can only be determined in the fourth month of pregnancy by methods such as ultrasonography and amniocentesis, and if a serious abnormality is detected, the pregnancy is terminated around the 5th month. This situation traumatizes the expectant mother and father psychologically and physically.
In recent years, developments in genetic science allow genetic examination to be carried out on embryos developed in the laboratory using in vitro fertilization methods, before pregnancy occurs, and the placement of selected healthy embryos into the uterus of the expectant mother. This method is called pre-pregnancy genetic diagnosis (Preimplantation Genetic Diagnosis-PGT).
Pre-pregnancy genetic diagnosis is carried out by taking a cell from the embryos that develop as a result of fertilization of the egg and sperm cells obtained from the expectant mother and father in a laboratory environment.
Special methods called Fluorescence In Situ Hybridization (FISH) or Polymerase Chain Reaction (PCR) are used for genetic diagnosis. Diagnosis of numerical chromosome disorders such as monosomy or trisomy (Down syndrome and other trisomies) and single gene diseases (such as hemophilia, Mediterranean anemia, cystic fibrosis, muscular dystrophies) in the unborn baby is possible with PGT. Thus, the birth of healthy babies is ensured by transferring disease-free, healthy embryos to the expectant mother.
Pre-pregnancy diagnosis:
-In couples who are carriers of a genetic or hereditary disease,
-In couples who have previously had a child or children with a genetic disease,
-Women in the older age group (37 years and above) accepted for assisted reproductive techniques,
-In couples with recurrent early pregnancy miscarriages,
-In couples who have not been able to achieve pregnancy with assisted reproductive techniques despite numerous applications or who have lost their pregnancies due to miscarriages,
-Chromosomal disorders or genetic diseases associated with severe male infertility,
-For the purpose of performing HLA genotyping (tissue typing),
-In the identification of diseases that show genetic predisposition, it is recommended to apply a pre-transfer diagnosis method and the chance of healthy pregnancy is increased.
The purpose of pre-pregnancy genetic diagnosis is primarily to identify genetic diseases at the embryo stage. However, PGT is also used in couples who will undergo in vitro fertilization techniques due to infertility problems. Today, around 50 genetic diseases can be identified with pre-pregnancy genetic diagnosis. Today, it has become possible to identify many hereditary diseases at the embryo level with the DNA analysis method. Individuals transmit the hereditary disease they carry to their children at varying rates. Therefore, identifying genetic diseases in couples and embryos is important for couples to have healthy children. Before examining the DNA structure of the gene of a hereditary disease, that gene region must be duplicated. Thanks to a special method called PCR, millions of copies of a certain genetic region can be obtained in a very short time and its structure can be examined. With the sequence analysis method, permanent changes called mutations that cause genetic diseases can be detected much more sensitively and effectively. In this system, DNA samples are first marked with some special dyes. The labeled DNA samples are then determined by a laser reader and the resulting data is transferred to the computer. Thus, the disorder in the genetic structure is determined.
In addition to hemophilia, diseases such as ß-thalassemia and sickle cell anemia, which are very common in Mediterranean societies and in our country, occur as a result of mutations in the ß globulin gene. Today, more than 300 mutations that cause these diseases have been identified. Thanks to the use of the sequence analysis method, most of the mutations in genetic diseases can be detected. With this method, in our center, the DNA of the cells taken from the embryos obtained by in vitro fertilization method of couples who are carriers of hereditary diseases is amplified by the "single cell PCR" method and the gene region of the screened disease can be identified by sequence analysis method.
ALSO IN THE EMBRYO OF COUPLES WITH NORMAL CHROMOSOME ANALYSIS
CAN GENETIC DISEASES BE OBSERVED?
Yes. In genetic tests performed on blood cells taken from couples, the chromosome structure may be found to be normal. However, the embryo receives half of its genetic structure from the mother's egg cell and the other half from the father's sperm cell. For this reason, although the genetic structure of the body cells is normal, some couples may have chromosomal disorders that can only be seen in the reproductive (egg or sperm) cells, and this disorder can be transferred to the embryos. Such genetic disorders in embryos can be detected with pre-pregnancy genetic diagnosis.
WHAT IS THE EFFECT OF CONSULTAN MARRIAGE ON THE EMERGENCE OF GENETIC DISEASES?
Consanguineous marriages are marriages made between people who are related by blood. According to the degree of kinship, the closest one is cousin marriages, which we call first degree consanguineous marriages, and they are marriages between the children of aunts, uncles and uncles. The rate of consanguineous marriage in our country is 21-40% and varies depending on the region. In general, anomalies resulting from various reasons are detected in 2-3 of every 100 children born in society. This risk may increase to 4-5% in couples who are married to consanguineous relatives.
As a result, while embryos carrying hereditary diseases are eliminated, healthy embryos can be transferred to give birth to children without genetic diseases. With the sequence analysis method, hereditary disease in muscle diseases such as thalassemia, cystic fibrosis and Duchenne muscular dystrophy, as well as hemophilia, can be identified at the embryo level.
In addition, in diseases such as thalassemia and leukemia, in addition to detecting healthy embryos by sequence analysis method, HLA genotyping (tissue typing) process can also be applied at the same time and the tissue type of the embryos can be determined. In families with children diagnosed with thalassemia or leukemia by HLA genotyping method, after determining the tissue types of the mother, father and child, embryos whose tissue type is compatible with the patient child can be selected among the embryos that do not carry the disease. Healthy pregnancies achieved in this way provide treatment for sick children by using the cord blood and bone marrow of healthy born children. With this method, the family is also protected from medical and psychological trauma due to pregnancy termination following the prenatal diagnosis process. Please click for more information about thalassemia disease and obtaining HLA compatible embryos.
Moreover; Pre-pregnancy diagnosis is a very important technique as it enables families to have healthy children and provides treatment opportunities for sick people due to the health problems that sick people face throughout their lives, difficulties in treating diseases and high treatment costs. As a result of current studies, it will be possible to identify many more diseases in embryos by determining the genetic structure of diseases.