Karyotype
Karyotyping, basic chromosome analysis prior to IVF, which ...
is required from both partners before the initiation of IVF,
should be a criterion for selection of assisted reproduction center,
reveals chromosomal rearrangements that cause infertility or repeated abortions or lead to the birth of a child with developmental abnormalities,
is performed from peripheral blood.
What is a chromosome?
Blood cells contain DNA bundled in their nucleus, which represents a carrier of genetic information. At a certain stage of cell division, DNA is visible in the form of fibrous, well-stainable formations. The assembly of these formations creates a human karyotype, and the procedure of its visualisation is called karyotyping. Examination and description of the human karyotype have specific international rules that are followed in all accredited cytogenetic laboratories.
What does a normal human karyotype look like?
Each human cell normally contains 46 chromosomes. But human chromosomes also differ. Twenty-two of these are called autosomes, one from each mother’s and father’s pairs. There are also two sex chromosomes called gonosomes, which are responsible for sex determination.
Numerical autosomal abnormalities
If one chromosome from the pair is missing, changes incompatible with life occur in the cells of the embryo and the embryo is aborted in the first trimester of its development.
If there is an extra one to those 22 chromosomes, the individual is born being more or less disabled, or his disability is incompatible with life. Disorders compatible with human viability include, for example, Down's syndrome, where there is an additional chromosome 21 in the karyotype. Thus, an individual has a total of 47 chromosomes instead of 46.
Numerical gonosomal abnormalities
When it comes to sex chromosomes, the situation gets more complicated. With an extra sex chromosome in his karyotype or the other way around, when one of the sex chromosomes is missing, the individual is more or less phenotypically (externally) normal, but very often infertile or his fertility is limited.
45, X Turner syndrome (woman missing second X chromosome)
47, XXY Klinefelter's syndrome (male has extra X chromosome)
Structural chromosomal abnormalities
Not only the number of chromosomes but also their structure is of utter importance. By examining the client’s karyotype prior to performing assisted reproductive treatment we are able to detect such structural disorders. The most common structural disorders include translocation, inversion, and deletion. Although the carrier of such a rearrangement is perfectly healthy, serious genetic problems may occur in his gametes and the couple is therefore exposed to unsuccessful conception attempts or even miscarriages and other complications.
Thanks to the examination of the karyotype, however, we are able to suggest to the clients, if necessary, another procedure and recommend, for example, preimplantation genetic testing. This makes the treatment safer and less invasive.
Currently, most translocations can be examined using the Next Generation Sequencing (NGS) method. The advantage of using the NGS method is that preimplantation testing of aneuploidies can also be performed at the same time as the translocation is determined.