PRE-IMPLANTATION GENETIC DIAGNOSIS

It is possible to diagnose genetic disorders during pregnancy or after birth. However, possible genetic disorders in the fetus can only be diagnosed in the fourth month of the pregnancy with methods like ultrasonography and amniocentesis, and pregnancies are terminated if a serious anomaly is found. This causes psychological and physical trauma in both partners.

The recent improvements in genetic sciences provides for genetic studies on embryos developed in laboratory conditions with IVF method and the chance of placing healthy embryos in the uterus of the future mother. This method is called genetic diagnosis before pregnancy (Preimplantation Genetic Diagnosis-PGD).

Preimplantation Genetic Diagnosis performed by fertilizing the ova and sperms in laboratory environment, and taking one cell from the embryos thus developed. Special methods like Fluorescence In Situ Hybridization (FISH) or Polimerase Chain Reaction (PCR) are used for Preimplantation genetic diagnosis. It is possible to diagnose number anomalies in chromosomes like monosomies and trisomies (Down syndrome and other trisomies) and single gene defects (Hemophilia, Mediterranean Anemia, cystic fibrosis, muscular dystrophies) with PGT. Birth of healthy babies thus achieved by the healthy transfer of healthy embryos to the future mother.

Biopsy performed on embryos

Pre-implantation diagnosis:

• Couples that are carriers of a genetic or hereditary disorder
• Couples that have a child or children with a genetic disorder.
• Assisted Reproductive Technologies (for women of advanced age 38 and over included in IVF method)
• For couples with repeated aborts in early stages of pregnancy
• For couples that the attempts for achieving pregnancy had failed or that the pregnancies achieved had terminated with aborts.
• In cases of chromosomal anomalies or genetic disorders that accompany serious male infertility
• With the purpose of HLA genotyping (tissue typing)
• With the purpose of defining disorders that show a genetic predisposition

are recommended to undergo preimplantation diagnostic procedures in order to improve the chance of a healthy pregnancy.

Three Chromosome 21 with preimplantation genetic diagnosis View from FISH analysis in an embryo with Down syndrome-Mongolism).

The purpose of preimplantation genetic diagnosis is to define the genetic disorders in embryonic stage primarily. However, PGT is also performed for the couples that IVF techniques will be applied to for infertility reasons. It is possible to define about 50 genetic disorders currently. Genetic disorders that are most frequently diagnosed with PGT are listed below:

	Thalassemia major (Mediterranean anemia)
	Congenital loss of hearing
	Cystic fibrosis
	Achondroplasia
	Duchenne muscular dystrophy
	Hemachromatosis
	Hemophilia
	Gaucher's Disease
	Sickle cell anemia
	Retinoblastoma
	Spinal muscular atrophy
	Fanconi Anemia
	Myotonic dystrophy
	Retinitis Pigmentosa
	Frajil X syndrome
	Epidermolisis Bullosa
	Phenylketonuria
	Neurofibromatosis
	Congenital adrenal hyperplasia
	ADA deficiency
	Alfa-1 antitripsin deficiency
	Tay-Sach's Disease
	Alzheimer
	Lesch Nyhan syndrome
	Huntington Disease
	Alport Disease

It is currently possible to define many hereditary disorders while in embryonic stage with DNA analysis. Individuals transfer their hereditary disorders in various ratios. So, it is important to diagnose genetic disorders in couples and in embryos to have healthy babies. The multiplication of a certain gene region is necessary before examining the DNA structure of a gene that transfers a genetic disorder. It is possible to obtain millions of copies of a certain genetic location in a very short time and to examine it with the help of a special method called PCR. These copied gene locations are subjected to sequencing procedure and thus all base sequences can be defined. With DNA sequencing method, permanent changes in genes that are called mutations and cause genetic disorders can be defined in a very accurate and efficient way. In this system, DNA samples are first labeled with some special dyes. Following this, the labeled DNA samples are defined with a special laser interpreter, and data obtained are transmitted to a computer. The defects in the genetic structure are thus defined. Diseases like ß-thalassemia and sickle cell anemia, which are seen frequently in Mediterranean communities and in our country, as well as hemophilia, are the results of mutations in ß-globulin gene. There are currently more than 300 mutations defined that cause these diseases. Much of these mutations seen in genetic disorders can be defined by using DNA sequencing method.

Defining of IVS I-110 mutation in an embryo with DNA sequencing Method

With this method, DNA of the cells taken from embryos formed by IVF method from cells of couples that are carriers of hereditary disorders, are multiplied with "single cell PCR" method, and the gene location of the disorder can be defined. As a result, embryos with that disorder are excluded, and healthy embryos are transferred, and thus healthy babies are born. Thalassemia, cystic fibrosis, and disorders that involve muscles like Duchenne muscular dystrophy can be diagnosed while in embryonic stage, as well as hemophilia with DNA sequencing method. Furthermore, with DNA sequencing method, it is possible to perform HLA genotyping (tissue typing) method simultaneously with the procedures performed to determine the healthy embryos, and to define the tissue type of the embryos in disorders like Beta-Thalassemia, Fanconi Anemia, and leukemia. Thus, with HLA genotyping method, embryos can be selected with a tissue type that matches that of a sick child in the family amongst the healthy embryos, for families with children with diseases like thalassemia or leukemia. Healthy pregnancies thus obtained can provide a chance for cure for the sick child by using the chord blood and bone marrow of the healthy baby. With this method, the family will be saved of the physical and psychological trauma of the termination of a pregnancy following a prenatal diagnostic procedure. Furthermore, preimplantation genetic diagnosis is a very important technique; since it ensures having healthy babies and saves the troubles of sick individuals like diagnostic difficulties, high costs of therapies, and at the same time, ensures the chance of cure to sick individuals. The researches that are being carried out currently will provide for determining the genetic structures of many more disorders, and also provide for defining these disorders in embryos.