What are preimplantation genetic tests?
Preimplantation genetic tests are methods for early testing of oocytes or embryos, in order to prevent the birth of children with genetic diseases, combining assisted reproductive technologies, embryology and genetics.Each normal embryo contains 46 chromosomes, 23 of which originate from the ovum, and the remaining 23 – from the sperm. Thus, an embryo containing 46 normal chromosomes is called an euploid embryo. Chromosomes are made up of genes that act as chemical messages that inform cells that they can and do function in different ways. There are more than 30,000 different genes, made up of DHK, inherited in a specific sequence and containing a “code” for each of them. There are serious consequences for the normal type (code), as well as the abnormalities in the genes or genes.
Preimplantation genetic tests are divided into two main groups – preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS). PGD сis used in families in which one or both parents have a proven genetic abnormality (chromosomal abnormality, monogenic defect or inherited disease in the genus transmitted by the X chromosome) and the embryo is tested for the specific mutation. In PGS, embryos of parents with a normal karyotype are screened for aneuploidy (incorrect number of chromosomes). Indications for PGS are advanced reproductive age of the woman, multiple miscarriages, failed attempts from previous IVF procedures, severe male infertility.
What is preimplantation genetic diagnosis(PGD)?
It is used for the establishment of translocations – changes in the type of chromosomes. Πpи пaциeнти c „бaлaнcиpaни” тpaнcлoĸaции oбиĸнoвeнo нe ce нaблюдaвaт пpoмeни, тъй ĸaтo нямa излишeн или липcвaщ xpoмoзoмeн мaтepиaл и нapyшeниeтo oбиĸнoвeнo нe paзcтpoйвa гeннaтa фyнĸция.In patients with “balanced” translocations, changes are not usually observed, as there is no excess or depletion of chromosome material and the intervention doesn’t disturb the genetic funcionality. It is typical for these patients that they do not have medical problems, despite the fact that some of them have reduced fertility. An “unbalanced” translocation is one in which there is an excess or lack of chromosome material. The probability of implantation of an embryo with an unbalanced translocation is small, the probability of abortion is higher, but if pregnancy occurs– it can lead to the birth of a living child, which is likely to have physical or mental problems. The initial translocations affect about 1 in 625 people. This type of translocation means writing in two different ways, allowing the parts between them to be altered. About 1 in 900 people have Robertson’s translocation, which includes chromosomes 13, 14, 15, 21 or 22. These chrpomosomes have larger lower halves, which can coalesce with each other. The risk of recurrent spontaneous abortions or malformations of the child is affected by the included x-ray (s) and the size of the altered fragment.Many single genetic defects can be identified through the use of RGD. These are diseases caused by inheritance of a single defective gene. There are two categories of single genetic defects:
- recessive – those in which two defective copies of this gene, one from each parent, are required to cause the disease.
- dominant – these for which, in order for the disease to appear, we need only one copy from the defective gene. It is suggested a pre-screening for some of the most common single gene defects like such as cystic fibrosis (CF) and Тау Ѕасhѕ disease in small populations.
Preimplantation genetic screening (PGS)
Indications for PGS are advanced reproductive age of the woman, multiple miscarriages, failed attempts from previous IVF procedures, severe male infertility.
In PGS, embryos are analyzed for the number of all chromosomes. Aneploidy is the most common chromosomal anomaly and represents the presence of an additional chromosome (trisomy) or a lack of a chromosome(monosomy). When there are additional or missing chromosomes, the probability of implantation decreases, and the percentage of spontaneous abortions increases. When chromosomes 13, 18, 21, X or У are affected an implantation can be made and the pregnancy may continue which can lead to birth of a child with chromosome disease. The most common trisomy is the Trisomy 21 or the Down Syndrome. The rest deviations include Patau syndrome (trisomy 13), Edwards syndrome(trisomy 18), Klinefelter syndrome (47 XXУ), Turner syndrome (45 X, lacking gender chromosome). Spontaneous abortions most often include trisomies 15, 16, 21, and 22. Most common anuploidy in 3 day embryos is 15, 16, 17, 21 and 22. The probability of aneyplodia increases with the advancement of the mother’s age. Since woman are born with their eggcell reserv for their entire life, it is considered, that the egg cells of women in advanced age is more likely to make mistakes when deviding of their chromosomes, which results in increased percentage of egg cells lacking or having additional chromosome. Studies show that more than 20% of embryos in women aged 35-39 years and 40-60% of embryos in women aged 40 and over are infected.At least 85% of embryonic aneuploidies occur in the ovum. Sperm aneuploidies have a much smaller proportion, amounting to about 7-8%. The remaining aberrations occur accidentally during cell division in the early embryonic stage.
What are the benefits of pre-implementation genetic testing?
- Selection and embryo transfer of these embryos, which do not contain absolute data for human abnormalities;
- reduction of spontaneous abortion;
- reduction of the many fertile pregnancies;
- increasing the rate of embryo implantation;
- raising the percentage of healthy children born.
What are the risks of pre-implementation genetic testing?
- damaged embryos (< 1%)
- error of diagnosis (false positive or negative) due to natural mosaicism on embryo or technical limitations on the method (<5%);
- lack of embryotransfer when detected 100% abnormal embryos (up to 20%).
Every case is individual and the need for diagnosis and treatment is different. Here you can find the pricing of all procedures that might interest you.
|1.||Chromosome analysis for 24 chromosomes (from 1 to 4 embryos) by the method of next generation on sequenting (NGS), included MitoScor for all genetically normal embryos||2990 BGN|
|2.||Chromosome analysis for 24 chromosomes (from 5 to 8 embryos) by the method of next generation on sequenting (NGS), included MitoScor for all genetically normal embryos||4350 BGN|
|3.||Chromosome analysis for 24 chromosomes (from 9 to 12 embryos) by the method of next generation on sequenting (NGS), included MitoScor for all genetically normal embryos||5930 BGN|
|4.||Chromosome analysis for 24 chromosomes ( 12+ embryos) by the method of next generation on sequenting (NGS), included MitoScor for all genetically normal embryos (every next)||490 BGN|
|5.||Embryonic biopsy for genetic analysis of 24 chromosomes||990 BGN|