Karyotype – is a set of chromosomes typical of a given organism and aligned according to standardised rules and recorded according to the rules of the International System of Cytogenetic Nomenclature ISCN. A karyotype test (cytogenetic testing) allows to assess whether cells of a given person show a normal number of chromosomes and whether their structure is normal. Diploid human body cells (somatic cells) have 23 pairs of homologous chromosomes, whereas reproductive cells are haploid and contain 23 chromosomes. A normal female karyotype is written as 46,XX, whereas a male karyotype is 46, XY.
Cytogenetic testing allows to detect numerical (monosomies, trisomies) or structural (deletions, translocations) chromosomal aberrations in a given patient. Clinical consequences of chromosomal aberrations include: in an embryo and foetus – death leading to miscarriage, in children born alive – presence of congenital defects combined with mental impairment (e.g. trisomy of chromosome 21 – Down syndrome), mental impairment with signs of dysmorphy or body and sexual disturbances (e.g. 45,X karyotype – Turner syndrome, 47,XXY – Klinefelter syndrome). Whereas in adults, a chromosomal aberration results in sterility (Turner syndrome, Klinefelter syndrome, women – 46,XY), a mutual translocation may be a reason for recurrent miscarriages or result in the birth of a child with numerous developmental defects or stillbirth. According to the literature data, 0.6% of children are born with a chromosomal aberration, and they are observed in 6% of cases of congenital developmental defects. On the other hand, balanced translocations are observed in 5% of couples with reproduction failures. The main indications for this test include: reproductive failures (miscarriages), giving birth to a child with congenital defects, male/female infertility of unknown aetiology, presence or suspicion of a disease conditioned by a chromosomal aberration based on a complex of clinical symptoms, and verification of a karyotype prior to the in vitro fertilization procedure. A karyotype is a constant parameter that does not change in the life so a karyotype test is performed once in a lifetime.
A karyotype test is performed according to the latest standards of the International System of Cytogenetic Nomenclature (ISCN) by specialists in laboratory clinical genetics and specialists in clinical genetics. A culture method includes a 3-day culture of lymphocytes and their growth is stimulated with phytohaemagglutinin.
As a standard, G-banding technique (Giemsa-Trypsin-Wrights) is used, and in selected cases C-banding, AgNOR and FISH techniques. 15 metaphases are analysed, but in specific cases even 50 to 100. An analysis of metaphases with the banding resolution of 400-550 is used, and in selected cases metaphases are analysed with high resolution (HRT) of >700 bands.
The karyotype test is performed with Cytovision and Metasystem software.