Human cytogenetics is an exam that aims to analyze chromosomes and thus identify chromosomal changes related to the patient's clinical characteristics. This test can be done at any age, even during pregnancy to check for possible genetic changes in the baby.
The chromosome is a structure made up of DNA and proteins that is distributed in cells in pairs, being 23 pairs. From the karyogram it is possible to identify changes in chromosomes, such as:
- Numerical changes, which are characterized by an increase or decrease in the amount of chromosomes, as in Down syndrome, in which the presence of three chromosomes 21 is verified, with the person having 47 chromosomes in total; Structural changes, in which there is replacement, exchange or elimination of a specific region of a chromosome, such as the Cri-du-Chat syndrome, which is characterized by a deletion of part of the chromosome 5.
Cytogenetics allows the environment and the patient to have an overview of the genome, helping the doctor to make the diagnosis and direct treatment, if necessary.
When is indicated
The examination of human cytogenetics can be indicated to investigate possible chromosomal changes, both in children and in adults. Thus, it may be asked to assist in the diagnosis of some types of cancer, mainly leukemias, and genetic diseases characterized by structural changes or by the increase or decrease in the number of chromosomes, such as Down syndrome, Patau syndrome and Cri-du-Chat, known as meow syndrome or cat scream. Learn more about cat meow syndrome.
How is done
The test is usually done from a blood sample. In the case of the examination in pregnant women whose purpose is to evaluate the fetus' 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 cultured so that they multiply and then an inhibitor of cell division is added, which makes the chromosome in its most condensed form and best viewed.
Depending on the purpose of the exam, different molecular techniques can be applied to obtain information about the person's karyotype, the most used being:
- Banding G: 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, mainly, and structural changes in 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: it is a more specific and sensitive technique, being more used to assist in the diagnosis of cancer, as it allows to identify small changes in chromosomes and rearrangements, in addition to also identifying numerical changes in chromosomes. Despite being quite effective, the FISH technique is more expensive, as it uses DNA probes labeled with fluorescence, requiring a device to capture the fluorescence and allow the visualization of chromosomes. In addition, there are more accessible techniques in molecular biology that allow the diagnosis of cancer. Learn more about how molecular diagnosis is done.
Following the application of the dye or marked probes, the chromosomes are organized according to size, in pairs, the last pair corresponding to the person's gender, and then compared with a normal karyogram, thus checking for possible changes.
The cytogenetics exam does not require any preparation and the collection is not delayed. The result, however, can take 3 to 10 days to be released according to the laboratory.
