Reconciling In Vitro Fertilization practices and genetic technology does not have a very long history. The applications, generally called preimplantation genetics, which started with determining the sex of the embryo in the early 1990s with the aim of preventing diseases transmitted through gender, have developed extremely rapidly and today allow the diagnosis of single gene diseases and tissue antigens at the embryo level. Preimplantation genetic applications are divided into two.
The first and most used of these is the application called preimplantation genetic screening (PGS), which is used to reveal structural and numerical disorders of chromosomes. Preimplantation genetic screening is done using a technology called FISH (flourescent in-situ hybridization). Under the fluorescence microscope, normal or abnormal structure and number of paired chromosomes can be seen with probes that give different color reflections. For example, the disease called Down syndrome, which is the most common cause of congenital retardation, occurs when there are three chromosomes 21 instead of two. When FISH is performed, 3 probes will be seen binding to chromosome 21. Thus, the embryo diagnosed with Down syndrome will not be placed in the uterus.
PGS has 3 main areas of use. These are advanced female age (after 38 years of age), the presence of a history of repeated miscarriages (3 or more miscarriages) and repeated in vitro fertilization failure (no pregnancy despite a total of 10 embryo transfers in 3 or more in vitro fertilization applications). However, PGS, in its current form, does not increase the rate of going home with a live baby in these 3 cases. The reason for failure in this current state is 1) evaluation of only a limited number of chromosomes with current technology, 2) FISH method gives false-negative and false-positive results; 3) the potential for embryo biopsy to damage the embryo. In fact, in a recent Dutch study, the pregnancy rate was found to be lower in the PGS arm compared to those without PGS, due to advanced female age. At our Center, we only perform PGD in cases with structural or numerical chromosome problems in male or female chromosome examination. PGS is t We do not prefer it.
Preimplantation genetic diagnosis (PGD) is based on the principle of recognizing diseases that are known to exist and are transmitted through a single gene. With a different technology called PCR, the change in the gene that causes the disease is detected at the embryo level and unhealthy embryos are not transferred. The number of single gene diseases that can be diagnosed with PGT is increasing day by day. Thalassemia, or Mediterranean anemia, is one of the most common single gene diseases that concern our country, and is the most commonly used PGT application. Apart from thalassemia, the diagnosis of many single gene diseases such as sickle cell anemia, Tay Sachs disease, Fragile X syndrome and many others is possible with PGT. With PGD, couples who have a diseased child can also have a histocompatible sibling for this child for transplantation with stem cells taken from bone marrow or cord blood. In this way, the couple can both have a healthy child and have a stem cell transplant for their diseased children.
With rapid advances in the field of genetic engineering, the repair of faulty genes will be possible in the not too distant future. Although determining the entire genetic structure at the embryo level and changing diseased genes may seem like a science fiction today, the possibility of these happening in the future seems high. Of course, these practices also have an ethical dimension that cannot be ignored. It is therefore very important to carefully examine its ethical dimensions.
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