What is a cytogenetic study?

Modern medicine can offer prospective parents not only to know the sex of the child and see his features, but also to determine in advance what diseases await their offspring in the future. The cytogenetic study helps in this. To do it, several milliliters of blood or any other liquid / tissue of the fetus is sufficient. After carrying out complex chemical and physical manipulations with the material, the geneticist can provide answers to questions of family interest.

Definition

Cytogenetic research is a microbiological study of a person's genetic material in order to identify gene, chromosomal or mitochondrial mutations, as well as oncological diseases. The value of this study is determined by the availability of cells for karyotyping and studying the changes occurring in them.

The appearance of the DNA molecule in the nucleus of the cell varies greatly depending on the phase of the cell cycle. In order to conduct the analysis, it is necessary that a conjugation of chromosomes takes place, which occurs in the metaphase of meiosis. With a qualitative fence of the material, each chromosome is visible as two separate chromatids located in the center of the cell. This is an ideal option to conduct a cytogenetic study. The human karyotype is normally composed of 22 pairs of autosomes and two sex chromosomes. In women it is XX, and for men it is ХУ.

Indications

Cytological research is conducted in the presence of specific indications from both parents and the child:

- male infertility;
- Primary amenorrhea;
- habitual miscarriage of pregnancy;
- stillbirth in the anamnesis;
- the presence of children with chromosomal abnormalities;
- the presence of children with developmental defects;
- Before the procedure of in vitro fertilization (IVF);
- a history of unsuccessful IVF.

For the fetus, there are separate indications:

- the presence of birth defects in the child;
- mental retardation;
- delay of psychomotor development;
- sex anomalies.

Blood and bone marrow examination

Cytogenetic investigation of blood and bone marrow is carried out to determine the karyotype, to identify quantitative and qualitative disorders in the structure of chromosomes, as well as confirm the oncological disease. Blood cells with nuclei (leukocytes) are cultured in a nutrient medium for three days, then fix the resulting material on a slide and examine under a microscope. At this stage, it is important to have a qualitative coloring of the fixed material and the level of training of the laboratory technician who will carry out the research.

For bone marrow analysis , you need to get at least twenty cells from the biopsy specimen. The sampling of the material must be carried out only in the conditions of the medical institution, since the procedure is painful, and in addition, sterile conditions are necessary to prevent infection of the puncture site.

Fetal examination

Cytogenetic examination of the fetus is appointed by a geneticist after consultation of the couple. There are several options for taking material for this analysis. The earliest is a biopsy of the placenta. The sampling of the material for the cytogenetic study of the chorion is carried out transvaginally, under the supervision of ultrasound. Aspiration needle takes several villi of the future placenta, which already contain the DNA of the embryo. The procedure can be performed from the 10th week of pregnancy. Starting from the third month, amniocentesis is allowed. This is the aspiration of the amniotic fluid, where the fetal epithelial cells are located, which can be used as a material for research.

The third option is cordocentesis. This procedure can harm the child, so the testimony should be strong enough. A needle is inserted through the anterior abdominal wall into the amniotic bladder, which then must enter the vein of the umbilical cord and take some of the blood. The whole procedure is performed under ultrasound control.

With the help of these methods, it is possible to determine the monogenic, chromosomal and mitochondrial pathologies of the unborn child and decide whether to prolong or terminate the pregnancy.

Analysis of tumor cells

Molecular-cytogenetic study of chromosomes of cancer cells is difficult due to their morphological changes, as well as poor distinguishability of the bands. This can be translocation, deletion, etc. At the modern level, in situ hybridization is used to study such samples (i.e., "in situ"). This allows to identify the location of chromosomes in any molecule of DNA or RNA. It is possible to search in this way and markers of other diseases. It is important that research can be carried out not only in the metaphase, but also in the interphase, which increases the amount of material.

The main hitch is precisely in cancer markers, since in each specific case it is necessary to prepare an individual sequence of nucleotides and multiply it. Then, after accumulating a sufficient amount of the DNA under investigation, hybridization is actually carried out. In the end, it is necessary to separate the areas that were identified, and to draw a conclusion about the results of the study.

Types of chromosome abnormalities

To date, there are several types of chromosomal abnormalities:

- monosomy - the presence of only one chromosome from the pair (Shereshevsky-Turner's disease);
- Trisomy - the addition of another chromosome (cider superwoman and superman, Down, Patau, Edwards);
- deletion - removal of the chromosome region (mosaic forms of chromosomal pathologies);
- duplication - duplication of a specific segment of the chromosomal arm;
- inversion - rotation of the chromosome segment by one hundred and eighty degrees;
- translocation - transfer of genomic regions from one chromosome to another.

Structural chromosome abnormalities are transmitted to the next generation and can accumulate, so the risk of having sick children increases. The material of cytogenetic studies is carefully studied for the presence of lesions, and it is concluded on the condition of the whole organism.

Clinical significance

A cell that has an acquired or congenital anomaly may become the precursor of an entire clan of cells that will form a tumor or a stigma of disembryogenesis. Timely detection of them contributes to early diagnosis and decision-making on further tactics of treatment. Cytogenetic research has enabled many married couples with defective recessive genes to give birth to healthy children, or, if this is not possible, to think about the procedure of IVF and surrogate motherhood.