A karyotype is a set of all chromosomes that are found in the nucleus of every somatic cell that has them, with a number and structure specific to each species. The karyotype test is a type of cytogenetic test that can detect abnormalities in the number (chromosomal numerical aberrations) and the structure of the chromosomes (chromosomal structural aberrations).

Karyotypecontains a complete, characteristic set of chromosomes. Chromosomes are structures made of DNA and proteins, in each nucleated cell of the human body there are 46 chromosomes, including 22 pairs of autosomes, and 1 pair of heterosomes, i.e. sex-determining chromosomes.

The karyotype test is a cytogenetic test that allows the detection of abnormalities in the number (chromosomal numerical aberrations) and the structure of the chromosomes (chromosomal structural aberrations).

Knowing your karyotype is particularly important for people who are trying to have children for a long time and unsuccessfully (in this case both partners should do them), women who have experienced miscarriages many times, or those who gave birth to a stillborn child, and people suffering from diseases genetically caused by chromosomal aberrations in order to confirm the diagnosis made on the basis of phenotypic features.

Contents:

  1. Correct karyotype
  2. Karyotype: test purpose
  3. Indications for determining and testing the karyotype
  4. Karyotype: research material
  5. How is the karyotype test done
  6. Presentation of the karyotype results
  7. Karyotype: time and price of the test

Correct karyotype

Normal human karyotype consists of 46 chromosomes, 23 of which are inherited from the mother (this is the nucleus of the female gamete cell nucleus - the egg cell), and 23 from the father (contained in the male gamete cell nucleus - the sperm).

Among the chromosome set there are 22 pairs of autosomes (responsible for the inheritance and transmission of all features except those related to sex) and 1 pair of heterosomes (responsible for the inheritance of sex-related features).

Karyotype is described by numbers, which represent the total number of chromosomes in the cellsomatic and capital letters X and Y which represent sex chromosomes.

Normal female karyotype is described as 46, XX (thus it consists of 46 chromosomes, of which 2 X chromosomes are sex-determining chromosomes), and normal male karyotype is described as 46, XY (similarly, it consists of 46 chromosomes, and gender is determined by two heterosomes, X and Y).

Karyotype: purpose of the cytogenetic test

Cytogenetic examination and karyotyping are performed in order to check whether the number and structure of the patient's chromosomes is correct. Abnormalities in the number of chromosomes are called chromosomal aberrations, among which the following are distinguished:

  • numerical chromosome aberrations

Disturbances in the number of chromosomes with normal morphology usually arise as a result of abnormal cell division. It is distinguished by:

  • Polyploid (euploid) cells, which are characterized by a multiplied number of haploid chromosomes (1n=23 chromosomes) typical for germ cells, e.g. triploid cells (3n=69 chromosomes; karyotype 69, XXY), tetraploid (4n=92 chromosomes; karyotype 92, XXXY). Such aberrations are not common, and in humans are usually lethal
  • Aneuploid cells, characterized by an increased or decreased number of single chromosomes with the correct structure. Such aberrations can affect both autosomes and sex-determining chromosomes. Examples of disease syndromes caused by an abnormal number of chromosomes in cells include: - monosomy - Turner syndrome 45, X0 (one sex chromosome is missing) - trisomy - Down syndrome 47, XX, +21 or 47, XY, +21 (additional chromosome in pair 21)
  • Structural chromosomal aberrations

They are disorders in the structure of chromosomes, the number of which in a somatic cell is correct. The most common are:

  • deletion (loss of a fragment of a chromosome arm)
  • duplication (duplication of a specific fragment of a chromosome arm)
  • insertion (insertion of an additional fragment of another chromosome into the short or long arm of the chromosome)
  • inversion (180 degrees of a part of a chromosome arm)
  • translocation (transfer of a part of a chromosome arm to another chromosome)
  • ring chromosomes (formed as a result of rupture and reconnection of broken ends of one or more chromosomes)

Indications for determining and testing the karyotype

Cytogenetic tests and karyotyping are performed both in adults and in trying couplesoffspring, pregnant women and children. There are many indications for such diagnostics, especially:

  • Reproductive failure

- infertility of a couple (defined as the lack of pregnancy despite regular intercourse 3-4 times a week for a period of at least 1 year, without the use of any form of contraception) - recurrent miscarriages and difficulties in maintaining pregnancy - stillbirth - stillbirth a child with a genetically determined disease related to the occurrence of abnormalities in the number or structure of chromosomes - examination of the karyotype of partners who want to undergo in vitro fertilization

  • Genetic prenatal diagnosis is indicated in the case of

- advanced mother's age (women over 35) at the time of pregnancy - abnormalities in the number or structure of chromosomes in the parents of the child or siblings - abnormal results of prenatal tests based on non-invasive techniques of fetal imaging with ultrasound, which may indicate an increased risk of chromosomal aberrations in the fetus (increased nuchal translucency, abnormal development of the nasal bone)

  • Diagnostics of diseases caused by chromosomal aberrations

- the patient has phenotypic features indicating the presence of a specific chromosome syndrome or dysmorphic features to confirm the diagnosis - the presence of diseases caused by chromosomal aberrations in the immediate family

  • Sex differentiation disorder

- abnormal structure of external genitalia making it impossible to clearly determine the sex of a newborn - no signs of sexual maturation

Karyotype: research material

The test material is usually:

  • Peripheral venous lymphocytes
  • Amniocytes, or exfoliated cells of the fetus found in the amniotic fluid of a pregnant woman. Their examination makes it possible to determine the karyotype of the fetus. Collection of amniotic fluid (amniocentesis, amniocentesis) is performed in specialized centers by a specially trained gynecologist under the supervision of ultrasound equipment. It consists in inserting a puncture needle through the mother's abdominal wall into the amniotic cavity and collecting 15-20 ml of amniotic fluid. It is an invasive test with many complications, including the risk of pregnancy loss, spotting from the genital tract, leakage of amniotic fluid, as well as intrauterine infection, intrauterine death, or puncture needle injury. They can be performed between the 15th and the 20th week of pregnancy.
  • Cellschorionic villus sampling
  • Chorionic villus sampling is performed between the 9th and 12th week of pregnancy. It is an invasive test with many complications, similar to an amniocentesis test.
  • Fetal blood cells collected during codrocentesis
  • Cordocentesis, i.e. puncturing the umbilical cord with a puncture needle under strict ultrasound control. It is performed after the 16th week of pregnancy in order to collect fetal blood for examination. It is an invasive test, performed rarely, and is associated with the possibility of many complications, similar to amniocentesis and chorionic villus sampling.
  • Fibroblasts obtained by tissue culture
  • Cells derived from cancerous tumors

How is the karyotype test done

Testing the complete set of chromosomes can be done by testing any nucleated cell in the body, but the most common use is peripheral blood lymphocytes.

A sample of a small amount of the patient's venous peripheral blood is collected as standard for a basic blood test, such as a complete blood count. No prior preparation of the patient for the examination is required, it can be performed at any time of the day, and the patient does not need to be on an empty stomach.

To perform a cytogenetic test, it is necessary to obtain from a blood sample lymphocytes inhibited in the appropriate phase of cell division (mitosis) - metaphase. For this purpose, the cells are cultured in in vitro conditions. With the use of cell division stimulators, they are stimulated to multiply.

When cells reach the metaphase stage of mitosis, a special substance is administered to inhibit the multiplication process in the selected stage of mitosis. At the metaphase stage, the chromosomes are best developed and the easiest way to analyze them in detail. The next step in the karyotype test is staining of the chromosomes in order to obtain the characteristic stripe pattern of each chromosome.

On this basis, the person conducting the analysis is able to recognize the corresponding chromosomes and divide them into homologous pairs. The analysis of the number and structure of chromosomes is possible thanks to the use of specialized equipment, an accurate light microscope and computer software.

Presentation of the karyotype results

The obtained and stained chromosomes must be recognized and divided into corresponding homologous pairs of chromosomes marked with numbers from 1 to 22. Their identification is possible thanks to the arrangement of bands in each pair, which is characteristic for each of the chromosomes. Heterosomes, or sex chromosomes, are marked with the letters X and Y.

The graphic distribution of 22 pairs of chromosomes and 1 pair of autosomes is called the karyogram. In order to perform it, it is necessary to make a photomicrograph of specially stained chromosomes arrested at the stage of mitotic metaphase. The obtained chromosomes are cut from the photos and arranged in homologous pairs according to their size, centromere position and stripe patterns.

Karyotype: time and price of the test

The cytogenetic test and the development of the karyotype usually take 2 to 4 weeks because it is required to establish an in vitro culture of the test cells and stop cell division at the appropriate stage.

The patient's karyotype can be marked both privately in the cytogenetic laboratory and reimbursed by the National He alth Fund.

The cost of the test performed in private conditions fluctuates around PLN 500, it may slightly differ depending on the laboratory in which it is performed.

Category:

Pregnant examinations