HLA (HLA-compatible sibling)

HLA Analysis using Preimplantation Genetic Testing:

This method is a very important technique for families who have an affected child with HLA (Human Leukocyte Antigen) compatibility and who want to have healthy children with stem cell transplantation. Considering that the chance of having a healthy child in the natural cycle is 25% and the probability of birth of the HLA-compatible sibling is 20%, an IVF cycle with HLA and PGT support for diagnostic purposes is recommended.

Today, allogeneic bone marrow transplantation is performed in the treatment of some hematopoietic diseases, including beta-thalassemia and leukemia. Transplantation procedures from HLA-compatible donors give successful results in the treatment of such diseases.

How is HLA-compatible PGT done?

In the evaluation of the blastomere / trophectoderm cells after the biopsy is taken, fragment analysis and genotypes of gene regions where the mutation is seen and A, B, C and DRB regions of the HLA gene are performed. By analysing at least 8 polymorphic STR markers in the HLA region, it is possible to increase the accuracy of the test by preventing errors caused by contamination and crossing-over between HLA genes.

Since the rate of HLA compatible and screened mutation healthy embryos is generally 3/16, It is important to obtain as many embryos as possible in IVF application.

SAFER RESULTS WITH TROFECTODERM BIOPSY

PGT errors are more common due to the limited initial DNA in PGT applications performed with Polar body and Blastomere samples. These risks are reduced since more cell sources (5-8) are studied in trophectoderm biopsy. In addition to these technical advantages, the biopsy performed in the blastocyst stage will increase the pregnancy rate due to the fact that it is analysedprogressively with the most distinguished embryo (competent embryo) and at the same time, it will reduce the cost of PGT due to the less embryos per patient.

Blastomere and trophectoderm biopsies are used in preimplantation embryo biopsies. However, since 60% of cleavage embryos show mosaicism, it creates the possibility of false positive or false negative results. In addition, most embryos evaluated as aneuploid in the cleavage stage were found to be euploid in the blastocyst stage due to self-correction. Since we labelled the embryo incorrectly in the early stages of development it also reduces the chances of a live birth of the application.

Mosaicism also occurs in blastocysts but has a low rate compared to cleavage embryos. In the study of Johnson, the rate of mosaicism between inner cell mass and trophectoderm and between trophectoderm fractions was reported as 3-9%.

At the same time, the rate of aneuploidy seen in blastocyst cells is quite low compared to the previous stages of early embryo. Biopsy of the cells that do not participate in embryo formation in the embryo on the fifth day is another advantage, and this negative factor in cleavage embryos also affects the clinical success of PGT. It is also a very advantageous method in terms of embryo injury as cells are not biopsied by the trophectoderm biopsy.