Modern medicine can offer future parents not only to find out the sex of the child and see his facial features, but also to determine in advance what diseases await their offspring in the future. Helps in this cytogenetic study. For its implementation, a few milliliters of blood or any other fluid / tissue of the fetus is enough. After carrying out complex chemical and physical manipulations with the material, a geneticist can give answers to questions of interest to the family.
Definition
Cytogenetic study is a microbiological study of human genetic material in order to detect gene, chromosomal or mitochondrial mutations, as well as oncological diseases. The significance 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 cell nucleus varies greatly depending on the phase of the cell cycle. In order to carry out the analysis, it is necessary that chromosome conjugation occurs, which occurs in the metaphase of meiosis. AtIn a qualitative sampling of 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 normally consists of 22 pairs of autosomes and two sex chromosomes. For women it is XX, and for men it is XY.
Indications
Cytological examination is carried out in the presence of specific indications from both the parents and the child:
- male infertility;
- primary amenorrhea;
- habitual miscarriage;
- history of stillbirth;
- presence of children with chromosomal abnormalities;
- the presence of children with malformations;
- before the procedure of in vitro fertilization (IVF);- the presence of a history of unsuccessful IVF.
There are separate indications for the fetus:
- the presence of malformations in the born child;
-mental retardation;
- psychomotor retardation;- gender anomalies.
Blood and bone marrow examination
Cytogenetic examination of blood and bone marrow is carried out to determine the karyotype, identify quantitative and qualitative disorders in the structure of chromosomes, and confirm cancer. Blood cells with nuclei (leukocytes) are cultivated in a nutrient medium for three days, then the resulting material is fixed on a glass slide and examined under a microscope. At this stage, it is important to qualitatively stain the fixedmaterial and the level of training of the laboratory assistant who will carry out the study.
For bone marrow analysis, at least twenty cells must be obtained from a biopsy. Material sampling should be carried out only in a 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 sampling material for this analysis. The earliest is a biopsy of the placenta. The sampling of material for a cytogenetic study of the chorion is carried out transvaginally, under ultrasound control. With an aspiration needle, several villi of the future placenta are taken, 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 amniotic fluid, where there are fetal epithelial cells that can be used as material for research.
The third option is cordocentesis. This procedure can harm the child, so the evidence must 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 carried out under ultrasound control.
Using these methods, it is possible to determine monogenic, chromosomal and mitochondrial pathologies of the unborn child and make a decision to prolong orabortion.
Tumor cell analysis
Molecular cytogenetic study of the chromosomes of cancer cells is difficult due to their morphological changes, as well as poor visibility of the bands. This can be a translocation, deletion, etc. At the present level, in situ hybridization (i.e., “in situ”) is used to study such samples. This allows you to identify the location of chromosomes in any DNA or RNA molecule. You can also look for markers of other diseases in this way. 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 problem lies precisely in the markers of oncological diseases, since in each case it is necessary to prepare an individual nucleotide sequence and multiply it. Then, after the accumulation of a sufficient amount of the studied DNA, hybridization itself is carried out. In the end, you need to separate the areas that were identified and draw a conclusion about the results of the study.
Types of chromosome disorders
Today, there are several types of chromosomal disorders:
- monosomy - the presence of only one chromosome from a pair (Shereshevsky-Turner disease);
- trisomy - the addition of one more chromosome (superwoman and superman cider, Down, Patau, Edwards);
- deletion - removal of a portion of a chromosome (mosaic forms of chromosomal pathologies);
- duplication - duplicationa certain section of the chromosome arm;
- inversion - rotation of a chromosome section by one hundred and eighty degrees; - translocation - transfer of genome sections from one chromosome to another.
Chromosome structural abnormalities are passed on 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 damage, and a conclusion is made about the state of the whole organism.
Clinical significance
A cell that has an acquired or congenital anomaly can become the precursor of a whole clan of cells that will form a tumor or dysembryogenesis stigma. Their timely detection contributes to early diagnosis and decision-making on further treatment tactics. Cytogenetic research has enabled many couples with defective recessive genes to give birth to he althy children or, if this is not possible, to consider IVF and surrogacy.
