CYTOGENETICS

These include both numerical variations of whole chromosomes and other intra- and inter-chromosomal abnormalities such as deletions, duplications, inversions, insertions and translocations. Indications for karyotype testing are abnormal phenotypic signs in the proband, abnormalities of growth and development, mental retardation in personal or family history, stillbirth and death of the newborn, sterile or infertile couples (repeated spontaneous abortions), positive family history of chromosomal aberrations, screening of gamete donors.

Most chromosomal abnormalities in the foetus are numerical abnormalities (aneuploidy) of chromosomes 13, 18, 21, X and Y. These include an extra copy (trisomy) of chromosome 21 (Down syndrome), chromosome 18 (Edwards syndrome), chromosome 13 (Patau syndrome), chromosome X (XXX syndrome and Klinefelter syndrome XXY) or a missing copy (monosomy) of chromosome X (Turner syndrome). In this way, deviations in the number of chromosomes as well as balanced and unbalanced chromosome aberrations (rearrangements) are determined.

Infertility and recurrent abortion can also be caused by carrying a balanced chromosome aberration - a rearrangement (genetic material is quantitatively preserved but also distributed on another chromosome) in one of the partners. This creates a risk of passing on the unbalanced form of aberration to the foetus, where the genetic material is either in excess or missing. If the quantity and quality of the genetic material (information) is not preserved, this means varying degrees of disability for the foetus, or the embryo may die at the very beginning of pregnancy. If one of the partners carries a balanced chromosome aberration, about half of the embryos will carry the unbalanced form, a quarter will have the balanced form of the aberration (same as one of the parents) and a quarter will be completely free of the chromosome aberration.

Type of material to be examined: blood, chorionic villi, amniotic fluid, fetal blood, product of conception (tissue from abortion)

Indicating specialists: medical genetics

These include occupational exposures (chemicals, radiation) or therapy with potential mutagens (ionizing radiation, cytostatics, immunosuppressants) and some viral infections (measles, rubella, smallpox). Clastogens can cause temporary or permanent genetic changes at the DNA level. Based on the evaluation of this test, the clinical geneticist can assess the actual risk to which the subjects are exposed. ACA testing is particularly important during the reproductive age, when there is a risk of gamete mutations and, in the case of pregnancy, direct mutagenic or teratogenic effects on the foetus. This is associated with an increased risk of miscarriage and congenital developmental defects in the foetus. In case of increased exposure to the above-mentioned influences, we recommend repeated ACA testing with a time gap to exclude environmental influences. The recurrence of an increased number of aberrant cells means an increased risk of cancer, a risk of faster cell ageing and an increased risk of birth defects in the offspring.

Type of material examined: peripheral blood

Indicating specialists: medical genetics

In this case, the number of fluorescent signals in individual cells is evaluated and possible gonosomal mosaicism or aneuploidy is determined. Minor variations in the number of sex chromosomes are also determined in this way. The rate of mosaicism is related to fertility disorders. Currently, about 15-20% of couples in the population is infertile. About 5-13% of infertility is caused by chromosomal aberrations.

The most common are numerical aberrations (aneuploidies) of sex chromosomes (gonosomes) causing known syndromes: in women Turner syndrome (45,X) and triple X syndrome (47,XXX), in men Klinefelter syndrome (47,XXY) or Jacobs syndrome (47,XYY). These syndromes very often occur in a mosaic form, which means that the numerical deviation is not present in all cells of the examined person, but only in some. This method can be used to evaluate a large number of cells (100-500) in a fluorescence microscope. Fluorescence signals on cell nuclei are also evaluated, whereas only chromosomes in mitosis can be evaluated in karyotyping - and there are usually only a limited number of these. This examination provides more accurate information on the degree of mosaicism (significantly reducing the risk of small number errors).

Type of material to be examined: blood, chorionic villi, amniotic fluid, fetal blood, product of conception (tissue from abortion)

Indicating specialists: medical genetics

Most fetal chromosomal abnormalities are due to numerical abnormalities of chromosomes 13, 18, 21, X and Y. These aneuploidies are also the cause of postnatal syndromes: Down syndrome (+21 chromosome), Patau syndrome (+13 chromosome), Edwards syndrome (+18 chromosome), Turner syndrome (45,X), triple X syndrome (47,XXX), Klinefelter syndrome (47,XXY) or Jacobs syndrome (47,XYY). The conventional diagnostic procedure is cell culture followed by karyotyping, which takes about 2-3 weeks. The QF-PCR (quantitative fluorescence PCR) method enables rapid prenatal detection of the most common aneuploidies (chromosomes 13, 18, 21, X and Y). However, the method does not completely replace conventional cytogenetic analysis, because it does not include the examination of the entire karyotype (structural chromosomal variations - translocations, inversions, insertions, deletions, and duplications). Since it is not necessary to use cultured cells, the main advantage of this method is speed. The usual time for issuing the result is within 24 to 48 hours, which will allow to relieve the stress of the parents, possibly extending the interval for deciding the further fate of the pregnancy.

Type of material to be examined: peripheral blood, chorionic villi, amniotic fluid, fetal blood, product of conception (tissue from abortion).
A buccal swab or maternal blood must also be provided for examination.

Indicating specialists: medical genetics

It is a reliable tool for detecting deletions and duplications across the entire human genome, capable of detecting aberrations up to 1,000 times smaller than in conventional karyotyping under a light microscope. The method is used in prenatal, postnatal and preimplantation diagnostics.

The method is based on the use of differentially labelled genomic DNA samples (patient, reference) that are simultaneously hybridized to DNA targets arrayed on a solid surface. Deleted or duplicated regions are detected according to the predominant fluorescence colour. Thousands to hundreds of thousands of hybridization reactions take place on the chip, the results of which are scanned by laser, analysed by software, and the findings are searched in databases and publications.

Findings of microdeletions or microduplications in the genome are beneficial in the diagnosis of specific and non-specific phenotypic manifestations and organ impairments, often associated with varying degrees of mental retardation. Deletion or duplication often affects many important genes. The test fails to detect balanced forms of chromosomal rearrangements, point mutations and low-frequency mosaics.

Type of material to be examined: blood, chorionic villi, amniotic fluid, fetal blood, product of conception (tissue from abortion)

Indicating specialists: medical genetics

However, the method does not completely replace conventional cytogenetic analysis, because it does not include the examination of the entire karyotype (structural chromosomal variations - translocations, inversions, insertions, deletions and duplications). Since it is not necessary to use cultured cells, the main advantage of this method is speed. The usual time for issuing the result is within 24 to 48 hours, which will allow to relieve the stress of the parents, possibly extending the interval for deciding the further fate of the pregnancy.

Type of material to be examined: peripheral blood, chorionic villi, amniotic fluid, fetal blood, product of conception (tissue from abortion). A buccal swab or maternal blood must also be provided for examination.

Indicating specialists: medical genetics