Why (and when) to do the karyotype examination

It consists of the analysis of chromosomes, which allows to identify abnormalities that can cause different types of diseases, hereditary and not.

The important thing is that it is healthy. It is the first thought when expecting a baby. For this reason, couples undergo genetic testing.

However, these tests must always be accompanied by the advice of a geneticist, who explains to the couple the meaning of the results reported on the report, the consequences in terms of risk and possible treatments. Otherwise, the results are not useful and only serve to generate anxiety and insecurity.

The most common examination is the analysis of the karyotype of aspiring parents, that is, the mapping of their chromosomes or cytogenetic analysis.

What is karyotype

The karyotype is the chromosomal makeup of a person, which derives 50% from the mother and 50% from the father. Every human being has in his DNA 46 chromosomes, divided into 23 pairs of autosomes, ie identical chromosomes, 22 of which are XX; the last couple establishes the sex of the person: XX for the woman, XY for the man.

During conception, a sperm with 23 chromosomes joins with an egg that contains 23 more, to give life to a human being with 46 chromosomes.

Before and after conception

The karyotype examination can be carried out for preventive purposes on the parents to check for the presence of abnormalities in the chromosomes that could be transmitted to the unborn child, as for example in the case of cystic fibrosis or thalassemia.

The examination is also often performed when a couple has reproductive problems as some chromosomal abnormalities can cause sterility or repeated miscarriages.

This test may also be useful once pregnancy has begun, to detect chromosomal abnormalities in the fetus. Karyotype analysis is usually recommended when the risk of abnormalities is higher than normal, for example if the mother is over 35 years old, in case of unfavorable results of a screening test or ultrasound during pregnancy, or if the parent couple already has a child with chromosomal abnormalities.

What does it consist of?

If the analysis is performed on the parents it is a simple blood sample (or more rarely bone marrow needle aspiration or bone marrow biopsy), while if you decide to analyze the chromosomes of the fetus, then it will be necessary to resort to an invasive prenatal test.

To know the genetic heritage of the unborn child, it will be necessary to take some of its cells from the placenta (or more precisely from the chorionic villi in which it branches) through a procedure known as chorionic villus sampling, or from the amniotic fluid through amniocentesis. To guide the choice between the two techniques is above all the stage of development of the fetus: chorionic villus sampling, in fact, is performed from week 10 to week 13, while amniocentesis can only be performed later, from week 15 to week 18.

Tests have also recently been developed to detect some specific chromosomal abnormalities from fetal cells present in maternal blood. Also in this case, a peripheral blood sample is usually carried out, which does not require any preparation (such as fasting).

The gynecologist will provide more information and useful information on the different methods to evaluate the pros and cons of each and decide which examination to undergo.

Once a sufficient sample of cells has been obtained from the parents or the fetus, they will be analyzed in the laboratory: first they will be cultured and then, if necessary, divided, because it is precisely during cell division that the chromosomes are best visualized. We will then proceed with the staining of the chromosomes and with a microscopic analysis (called chromosomal analysis or karyotyping) that will allow to identify any alterations in the number or structure. In this phase the chromosomes will be analyzed, counted and finally photographed, in order to obtain images to be “cropped” and then recomposed according to some characteristics (such as size, position of the throttling and banding).

Smaller abnormalities can be detected by special genetic testing that includes specific tests such as chromosomal microarray (CMA) and fluorescence in situ hybridization (FISH).

The results are obtained after about two to three weeks. If the exam is performed in a public or private structure affiliated it is free or subject to the payment of a ticket, while in private facilities the exam is paid and the price may vary.

What you “see”

The examination identifies two types of problems: if the result indicates a numerical anomaly, it means that there is a different number of chromosomes (more or less) than the 46 characteristic of the human being. An example of these chromosomal abnormalities (called anueploidy in medicine) are trisomies, which involve the presence of three copies of the same chromosome (instead of two), as happens in the trisomy of chromosome 21, which causes Down syndrome, and in those of chromosomes 13 and 18, which cause Patau and Edwards syndromes respectively.

Another case of numerical abnormalities are monosomes, i.e. the lack of a chromosome: this is what is observed in subjects with Turner syndrome, in which there is only one sex chromosome (X) instead of two.

Especially if they do not concern the sex chromosomes (as happens in the case of Klinefelter syndrome), numerical abnormalities often do not allow the survival of the embryo, and cause a spontaneous interruption of pregnancy.

The alterations can also affect the structure of chromosomes, and are divided into:

Deletions	Loss of a chromosome fragment.
Inversions	Detachment of a chromosome fragment that inserts itself again in the same place, but rotated 180 degrees.
Duplication	Doubling of a chromosome fragment.
Translocations	Exchange of a fragment between two different chromosomes.