General Practice 2022

Citogenética: what é, like é made and what is it for

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Citogenética: what é, like é made and what is it for
Citogenética: what é, like é made and what is it for

The cytogenetic exam aims to analyze the chromosomes and, thus, identify chromosomal alterations related to the clinical characteristics of the person. This test can be done at any age, even during pregnancy to check for possible genetic changes in the baby.

Cytogenetics allows the doctor and patient to have an overview of the genome, helping the doctor to make the diagnosis and direct the treatment, if necessary. This exam does not require any preparation and the collection does not take long to be done, however the result may take between 3 and 10 days to be released according to the laboratory.

What is it for

The human cytogenetic exam may be indicated to investigate possible chromosomal alterations, both in children and adults. This is because it evaluates the chromosome, which is a structure made up of DNA and proteins that is distributed in pairs in cells, with 23 pairs. From the karyogram, which corresponds to the chromosome organization scheme according to their characteristics that is released as a result of the exam, it is possible to identify alterations in the chromosomes, such as:

  • Numerical alterations, which are characterized by an increase or decrease in the number of chromosomes, such as what happens in Down syndrome, in which the presence of three chromosomes 21 is verified, the person having 47 chromosomes in total;
  • Structural alterations, in which there is replacement, exchange or elimination of a certain region of a chromosome, such as Cri-du-Chat syndrome, which is characterized by a deletion of part of chromosome 5.

Thus, it can be requested to help the diagnosis of some types of cancer, mainly leukemias, and genetic diseases characterized by structural alterations or by the increase or decrease in the number of chromosomes, such as Down syndrome, Patau and the Cri-du-Chat syndrome, known as the cat's meow or scream syndrome.

How it's made

The test is usually performed from a blood sample. In the case of the exam in pregnant women whose objective is to evaluate the fetal chromosomes, amniotic fluid or even small amounts of blood are collected. After collecting the biological material and sending it to the laboratory, the cells will be cultivated so that they multiply and then an inhibitor of cell division is added, which makes the chromosome is in its most condensed form and with better visualization..

Depending on the purpose of the exam, different molecular techniques can be applied to obtain information on the person's karyotype, the most used being:

  • G Banding: is a technique most used in cytogenetics and consists of the application of a dye, the Giemsa dye, to allow the visualization of chromosomes. This technique is very effective to detect numerical alterations, mainly, and structural alterations of the chromosome, being the main molecular technique applied in cytogenetics for the diagnosis and confirmation of Down syndrome, for example, which is characterized by the presence of an extra chromosome;
  • FISH technique: is a more specific and sensitive technique, being more used to aid in the diagnosis of cancer, as it allows the identification of small alterations in chromosomes and rearrangements, in addition to identifying also numerical alterations of the chromosomes. Despite being quite effective, the FISH technique is more expensive, as it uses fluorescence-labeled DNA probes, requiring a device to capture the fluorescence and allow the visualization of the chromosomes.In addition, there are more accessible techniques in molecular biology that allow the diagnosis of cancer.

Following the application of the dye or labeled probes, the chromosomes are organized according to size, in pairs, with the last pair corresponding to the person's sex, and then compared with a normal karyogram, thus verifying possible changes.

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