What determines a karyotype. Genetic examination of spouses when planning pregnancy. What this study can and cannot determine

Karyotype is the name of the type of chromosomes characteristic of a given biological species, and its determination is of great importance in a comprehensive examination of the reproductive system of a couple. To determine this, a special molecular analysis is required, which gives a complete picture of the genetic characteristics of a given couple, and based on this picture, options for solving problems are proposed. This test is a study of the shape, number and size of chromosomes in a sample of cells.

The presence of additional chromosomes or parts thereof, the absence of a chromosome or part of any of them can cause problems with the development of the functions of organs and systems. Even a completely healthy person can be a carrier of chromosomal rearrangements, although there are no visible signs of their presence. Because of them, there may be problems with pregnancy, infertility, and congenital malformations of the embryo.

Why do a blood test for karyotype?

First, a blood test helps determine pathologies in the chromosome set of a pair - translocation, mosaicism, deletion, monosomy, trisomy, etc.

This chromosomal analysis is done to find out what is the cause of congenital diseases or defects in the child; whether a chromosome defect causes infertility or miscarriage; whether the fetus has abnormal chromosomes; Are the chromosomes of an adult abnormal, and what effect do they have on his and the unborn child’s health; determine the sex of a person through the presence or absence of the Y chromosome (for example, if the sex of the child is not clear); to help select appropriate treatment for certain types of tumors.

Already in the early stages of pregnancy, those genetic changes that are characteristic of the fetus are visible: Patau, Shereshevsky-Turner, Down, Klinefelter, Edwards, Prader-Willi syndromes, autism and other serious developmental defects.

Who needs chromosome analysis?

In theory, every couple is shown this analysis, since none of us can vouch for our genes.

As a person ages, the likelihood of chromosomal changes increases, so if a husband and wife are over 35 years old, a chromosomal analysis is indicated for them. In the case of frequently recurring spontaneous abortions, arrest of fetal development, or inability to conceive, such a blood test is also done for both partners. When there is already a child with developmental problems, and a second pregnancy is planned, the husband and wife definitely need to check the karyotype. Well, it is clear that if there are relatives with genetic changes in the set of chromosomes, or a person is constantly under the influence of harmful factors (chemical, physical, radiation), this test must be taken without question.

This type of analysis helps identify:

anueploidy – that is, a change in the number of chromosomes towards an increase/decrease from the norm. True, they can be difficult to determine in the case of low-level mosaicism (when the body contains cells with an altered set of chromosomes in a small number along with normal cells). Although, aneuploidies occupy a small part both in the structure of genetic pathology in general and among the causes of congenital malformations;
structural abnormalities of chromosomes - joining in an abnormal combination after a break. In this case, karyotype studies can only detect large anomalies, but such changes are accessible to the fluorescent hybridization method and special chromosomal microarray analysis.

Donating blood for analysis

No special preparation is required, the main thing is to find an experienced geneticist who will help you understand, explain everything, weigh the risks, and make the right decision.

With the classic test (which has 5 subtypes), an amount of blood of about 10-20 ml is taken from a vein, and the cells are cultured and fixed. Next, the chromosomes are stained and examined using light microscopy. If this is a case of prenatal diagnosis, the analysis is done on cells obtained from the placenta or amniotic fluid. Sometimes bone marrow cells are tested.

There is also SKY (spectral karyotyping) - this is a completely new, highly effective method for studying chromosomes, which quickly and clearly identifies chromosomal abnormalities in cases where it is impossible to establish the origin of chromosomal material using standard karyotyping methods. The method is based on 24-color fluorescent staining of whole chromosomes.

SKY is an excellent tool for chromosome markers, clinical chromosomal translocation analysis, complex interchromosomal rearrangements, and finds multiple chromosomal abnormalities.

The Fish analysis method (fluorescence hybridization) is another modern effective way to study numerical abnormalities in chromosomes and complex abnormalities in the karyotype. In this type of analysis, the basis is the specific binding of fluorescent tags and specific chromosome regions. This approach makes it possible to test a larger number of cells than with classical karyotyping, since, although it is carried out on blood cells, it does not require their cultivation. The material for Fish analysis can be fetal, embryonic or sperm cells.

Karyotype analysis is a study that is carried out in a laboratory to identify pathologies in the structure and structure of chromosomes that can cause infertility or congenital diseases in children.

The essence of the classic karyotype analysis is to take blood from a vein with further screening out mononuclear leukocytes from it and attaching active cells that have the ability to divide. At the right time, the specialist stops division, stains the resulting cells, examines them under a microscope and photographs them. The results of the analysis can be found out after 2 weeks. They will indicate the number of chromosomes and the abnormalities that they contain. data-lazy-type="image" data-src="https://au-e.ru/wp-content/uploads/2015/12/kariotip.jpg" alt="karyotype" width="640" height="480"> !}

A blood karyotype test can be performed on both adults and children. Most often it is performed on married couples to identify the causes of infertility. In men, sperm pathology may be an indication for analysis. In women, karyotype analysis is recommended for menstrual disorders, miscarriages and stillbirths.

Karyotyping is also recommended for couples who have children with genetic disorders, such as Down syndrome, or abnormalities that arose during fetal development. Karyotype analysis is mandatory for couples before IVF.

For children, analysis is carried out for congenital developmental anomalies, mental retardation or infantilism. For newborns, an analysis is carried out to determine the sex of the child if it cannot be determined. This happens with false hermaphroditism.

Preparation for karyotyping

Karyotype analysis can be prescribed by doctors from various branches of medicine. But regardless of who prescribed the procedure, the results are deciphered by a geneticist. Therefore, at the initial stage of family planning, it is he who should be visited. data-lazy-type="image" data-src="https://au-e.ru/wp-content/uploads/2015/12/kariotp_2.jpg" alt="karyotyping" width="640" height="480"> !}
This doctor will be able to identify all possible risks, correctly diagnose and find the most appropriate solution to the problem. You can donate blood for analysis in any laboratory. The procedure itself is absolutely painless, but you should prepare before doing it.

Usually venous blood is taken for analysis, but in some situations biological material may be collected from other sources.

Preparing for the analysis is not difficult. 9-11 hours before blood sampling, you must stop eating and not drink liquid for 2-3 hours. No diets or nutritional regimens are required. It is recommended to stop smoking and drinking alcohol 2-3 months before the procedure. In addition, it is not recommended to take any medications, and if it is impossible to refuse medications, then you should definitely warn your doctor about this.

If a person is currently being treated for malignant tumors or other serious diseases, then a karyotype test is not recommended, since heavy drugs have the ability to damage chromosomes.

Types of diagnostics

There are several types of karyotyping. All these methods have different approaches to research and sources of biomaterial: data-lazy-type="image" data-src="https://au-e.ru/wp-content/uploads/2015/12/kariotip_5.jpg" alt="karyotype diagnostics" width="638" height="421"> !}

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It often happens that to clarify the situation, doctors, in addition to karyotyping, may prescribe other tests. If the results are unsatisfactory, then it is possible that not only the patient, but also his parents and children will have to undergo examinations.

Specifics of results

The karyotype has certain norms. So, for example, in representatives of both sexes the number of sex chromosomes should be 46. Usually, a karyotype examination is of systemic importance. This analysis is especially important if any chromosomal defects are detected in the blood. If the study is done during pregnancy, then for the most accurate result it may be necessary to collect biological material from other sources. This is necessary to identify fetal developmental disorders.

Deviations from the normal human karyotype can be found in one or both spouses. Therefore, when a couple is planning a family, they should be prepared for the fact that both the man and the woman may have to undergo genetic tests.

Genetic diagnostics occupies a special position in modern medicine. It allows you to clearly identify congenital malformations and predisposition to them. Karyotype analysis is one of the most popular methods for such diagnostics.

This concept was introduced by the Soviet scientist Grigory Levitsky at the beginning of the twentieth century. It includes the totality of all the characteristics of a set of chromosomes inherent in the cells of a particular biological species, and in this case the human body.

Normally, a person's karyotype is determined by 46 chromosomes, organized into 23 pairs. In each pair, one of them is transmitted from the mother, and the other from the father.

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If in this structure crash occurs(one chromosome is missing or an extra one appears), the child develops developmental abnormalities.

Blood analysis

The study allows us to identify abnormalities in the number and structure of chromosomes, which could lead to the occurrence of hereditary diseases, the birth of a child with developmental disabilities to spouses, and cause infertility (both female and male).

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Anna Poniaeva. She graduated from the Nizhny Novgorod Medical Academy (2007-2014) and Residency in Clinical Laboratory Diagnostics (2014-2016).

Karyotyping - the procedure is long and complicated Therefore, it is advisable to carry it out only in specialized laboratories, reproductive centers, and genetics institutes.

How is diagnostics carried out?

Material for research any dividing cells can act, obtained from the epidermis, bone marrow, through the placenta (during the development of the fetus in the womb), but more often from the blood (lymphocytes).

Venous blood is collected from the patient, which is placed in a test tube and sent to the laboratory for testing.
Lymphocytes are separated from the resulting material, placed in a test tube, and a substance (mitogens) is added that causes them to actively divide.
Then another substance (colchicine) is added, which stops cell division at the metaphase stage.
The results obtained are recorded, stained with a special solution (dye) and photographed. The entire procedure is carried out under a microscope.
From the set of photographs obtained, a karyotype or a numbered set of homologous chromosomes is formed. Having arranged them in pairs, the specialist analyzes them.

Preparing for the study

Diagnostics does not require special training. At the same time, the patient needs to understand that the procedure is performed only once in a lifetime, since the karyotype does not change over time. Therefore, experts advise adhering to some rules before taking the test:

It is not recommended to donate blood on an empty stomach, unlike many other types of research.
For 3-4 weeks, the use of antibiotics is excluded.
Be sure to get a good night's sleep the night before the test and eliminate the influence of stressful situations.

Indications for the procedure

Genetic diagnostics can be performed if there are certain medical indications or without them (at the request of the spouses).

Indications for diagnostics:

Unsuccessful pregnancy in women, repeated several times in a row for no apparent reason (fetal fading, miscarriage).
Suspicion of infertility of the father or mother (both spouses, regardless of gender).
Intrauterine fetal death.
The birth of a child with serious hereditary diseases and developmental abnormalities.

What can a karyotype determine?

The results of the study may show:

The risk of having a child with pathologies in development (when studying the karyotype of spouses).
The cause of a congenital childhood anomaly (mental retardation, mental retardation).
Recognition of chromosomal diseases of the fetus (Down syndrome, Patau and others).

Using karyotyping, you can clearly trace the structure of the chromosome set and identify:

Reversal of a chromosomal region (inversion).
Loss of a section of a chromosome or deletion.
The presence of an extra 3rd chromosome in a pair (trisomy), which occurs in Down syndrome.
Duplication of a fragment in a chain (monosomy).
Movement of sections in the structure of chromosomes (castling).

What can't it show?

Despite the depth of the analysis, it will not be able to recognize some deviations from the norm, namely:

The position of any individual genes in the DNA chain.
Exact number of genes in chromosomes.
Minor gene mutations that cause fetal pathology.

Analysis results

The standard results are:

* 46, XY, which corresponds to a normal male karyotype.
* 46, XX, which corresponds to a normal female karyotype.

Such values also apply to the study of children according to the sex of the child. The specialist records any other options according to the form of the international cytogenetic nomenclature and makes a decoding based on the accepted values, for example: 47, XX, +21; 47, XY,+21 (developing Down syndrome in the fetus - Trisomy on the 21st chromosome), 47, XX,+13; 47, XY,+13 (Patau syndrome in the fetus), etc.

Where to do the analysis?

Karyotyping - expensive and time-consuming process. In district clinics it will not be possible to donate blood for this test due to the lack of special specialists and equipment. Diagnostics can be carried out in family planning centers, genetic institutes, wide-profile laboratories, mother and child centers, and some modern clinics.

In Moscow, the service is provided by: Invitro, Family Clinic Doctor Anna, VitroClinic, Center for Molecular Diagnostics CMD, Laboratory CIR, Center for Maternal and Child Health named after V.I. Kulakova, Center for Fetal Medicine and others.
In St. Petersburg, the service is provided by: Genesis Reproduction Center, Mother and Child Clinic, EmbryLife Reproductive Technologies Clinic, Mother and Child Clinic, Invitro, Ava-Peter Clinic and others.

Price and lead time for analysis

Karyotyping refers to expensive diagnostic methods. Approximate cost:

Study of the karyotype of one patient (blood with heparin) - 4500-7500 rubles.
Taking a blood test for a karyotype with photographs of chromosomes costs 5,000-8,000 rubles.
Karyotyping with detection of aberrations (blood with heparin) is a more informative analysis, but its cost is more expensive - from 5500-6000 rubles.
Karyotyping with identification of aberrations with photographs of chromosomes - from about 6,000 rubles.

The deadline for preparing the analysis must be clarified at the place where the diagnostics will be carried out. Usually it ranges from 14 to 28 days (excluding the day the material was taken).

A blood karyotype test is an important modern diagnostic procedure. It allows you to accurately assess the number and structure of chromosomes in the human body. This will help to find out the causes of congenital anomalies in the fetus and genetic hereditary diseases.

Karyotyping is an analysis to identify chromosomal abnormalities, which is carried out to determine abnormalities in the number and structure of chromosomes. This research method can be included in the general list of examinations that are prescribed to couples before planning conception. Its implementation is an important part of the diagnosis, since the results make it possible to identify chromosomal abnormalities that interfere with conception, pregnancy and cause severe abnormalities in the development of the fetus.

For karyotyping analysis, both venous blood (sometimes bone marrow or skin cells) of the parents and fragments of the placenta or amniotic fluid can be used. It is especially important to carry out these if there is a high risk of transmitting chromosomal pathologies to the unborn child (for example, if one of the relatives is diagnosed with Edwards, Patau, etc.).

What is a karyotype? Who should undergo karyotyping? How is this analysis carried out? What can it reveal? You will get answers to these and other popular questions by reading this article.

What is a karyotype?

A karyotype is a qualitative and quantitative set of chromosomes.

A karyotype is a set of chromosomes in a human cell. Normally, it includes 46 (23 pairs) of chromosomes, 44 (22 pairs) of them are autosomal and have the same structure in both male and female bodies. One pair of chromosomes differs in structure and determines the sex of the unborn child. In women it is represented by XX chromosomes, and in men it is represented by XY chromosomes. The normal karyotype in women is 46, XX, and in men - 46, XY.

Each chromosome consists of genes that determine heredity. Throughout life, the karyotype does not change, and that is why you can take an analysis to determine it once.

The essence of the method

To determine the karyotype, a culture of cells taken from a person is used, which is studied in vitro (i.e., in a test tube). After the necessary cells (blood lymphocytes, skin cells or bone marrow) are isolated, a substance is added to them for their active reproduction. Such cells are kept in an incubator for some time, and then colchicine is added to them, which stops their division in metaphase. After this, the material is stained with a dye that clearly visualizes chromosomes and examined under a microscope.

Chromosomes are photographed, numbered, arranged in pairs in the form of a karyogram, and analyzed. Chromosome numbers are assigned in descending order of size. The last number is assigned to the sex chromosomes.

Indications

Karyotyping is usually recommended at the stage of conception planning - this approach helps minimize the risk of having a child with hereditary pathologies. However, in some cases, this analysis becomes possible after pregnancy. At this stage, karyotyping makes it possible to determine the risks of inheriting a particular pathology or is performed on fetal cells (prenatal karyotyping) in order to identify an already inherited developmental abnormality (for example, Down syndrome).

the age of the spouses is over 35 years;
the presence in the family history of a woman or man of cases of chromosomal pathologies (Down syndrome, Patau, Edwards, etc.);
prolonged absence of conception for unknown reasons;
planning;
previously performed unsuccessful IVF procedures;
bad habits or taking certain medications by the expectant mother;
hormonal imbalance in women;
frequent contact with ionizing radiation and harmful chemicals;
women have a history of spontaneous abortion;
history of stillbirth;
the presence of children with hereditary diseases;
history of episodes of early infant mortality;
caused by disturbances in sperm development;
marriage between close relatives.

fetal development abnormalities;
deviations of psychomotor or psycho-speech development in combination with microanomalies;
congenital malformations;
mental retardation;
growth retardation;
deviations in sexual development.

How is the analysis carried out?

drinking alcohol;
taking certain medications (especially antibiotics);
acute infectious diseases or exacerbation of chronic pathologies.

Blood sampling from a vein for analysis is performed in the morning when the patient is well-fed. It is not recommended to donate biomaterial on an empty stomach. When collecting tissue samples for fetal karyotyping, sampling is carried out under ultrasound guidance.

How long to wait for the result?

The result of karyotyping can be obtained 5-7 days after submitting the material for research. During this time, specialists observe cell division in the incubator, inhibit their development at a certain point, analyze the resulting material, combine the data into a single cytogenetic scheme, compare it with the norm and draw up a conclusion.

What can karyotyping reveal?

The analysis allows you to determine:

shape, size and structure of chromosomes;
primary and secondary constrictions between paired chromosomes;
heterogeneity of areas.

The results of karyotyping according to the generally accepted international scheme indicate:

number of chromosomes;
belonging to autosomes or sex chromosomes;
structural features of chromosomes.

Karyotype examination allows us to identify:

trisomy (or the presence of a third chromosome in a pair) - detected in Down syndrome, with trisomy on chromosome 13, Patau syndrome develops, with an increase in the number on chromosome 18, Edwards syndrome occurs, with the appearance of an extra X chromosome, Klinefelter syndrome is detected;
monosomy – absence of one chromosome in a pair;
deletion – lack of a section of a chromosome;
inversion – reversal of a chromosome section;
translocation – movement of chromosome sections.

Karyotyping allows you to identify the following pathologies:

chromosomal syndromes: Down, Patau, Klinefelter, Edwards;
mutations that provoke increased thrombus formation and premature termination of pregnancy;
gene mutations, when the body is unable to detoxify (neutralize toxic agents);
changes in the Y chromosome;
tendency to and;
tendency to.

What to do if deviations are detected?

The doctor provides patients with information about the results of karyotyping, but the decision about whether to continue the pregnancy is made only by the parents themselves.

When detecting abnormalities in the karyotype, the doctor explains to the patient the features of the detected pathology and talks about the nature of its impact on the child’s life. Particular attention is paid to incurable chromosomal and gene abnormalities. The decision on the advisability of continuing the pregnancy is made exclusively by the parents of the unborn baby, and the doctor only provides the necessary information about the pathology.

If a tendency to develop certain diseases (for example, myocardial infarction, diabetes mellitus or hypertension) is identified, attempts may be made to prevent them in the future.

Karyotyping is the analysis of a person's chromosome set. This test is done by examining lymphocytes in the blood, bone marrow cells, skin, amniotic fluid, or placenta. Its implementation is indicated at the stage of planning conception, but if necessary, the analysis can be carried out during pregnancy (on samples of cells from the parents or fetus) or on an already born child. The results of karyotyping make it possible to detect the risk of developing chromosomal and genetic pathologies and identify predisposition to certain diseases.

To determine the cause of infertility, a diagnostic method is used - a blood karyotype test. Starting a family is a responsible step, but on this path there is often such an obstacle as infertility.

This type of analysis refers to molecular genetic research. The principle of this examination is to study the structure of the genetic material, since the cause of infertility may be hidden in the characteristics of the DNA molecule.

A karyotype test is a kind of test for the compatibility of spouses. The results of the examination provide a small opportunity to change the current situation, create a full-fledged family by conceiving your child.

The biomaterial for research is blood samples. Leukocytes are extracted from plasma. To this element are added other cells that are constantly in a state of division. When two such components are mixed, the fission process stops. It is in this state that the resulting biological mixture is fixed under a microscope, tinted with special dyes and the result obtained is photographed.

This test allows specialists to get a fairly detailed picture of the existing chromosome combinations and their variants, since they are different for each person. Various abnormalities identified in chromosomal structures determine the causes of infertility, as well as options and possibilities for correcting the situation.

In the process of analyzing the collected biomaterial, a comprehensive study takes place, including the detection and determination of the characteristics of all indicators related to such a genetic component as a chromosome. Experts evaluate its shape, quantity, size and other data. Quite often, identified abnormal elements or additional types of chromosomes indicate various disorders. Such deviations may be associated with disruption of the functioning of various internal systems and organs of the subject.

Even a person with normal health can have chromosomal structures with unnatural rearrangements that do not affect the person being examined. But such deviations can affect the possibility of conception, pregnancy and fetal development.

Chromosome analysis allows us to identify possible defects that the unborn child may inherit. These are mainly rare diseases and certain congenital pathologies. This type of examination is necessary for couples suffering from infertility, frequent miscarriages, or seeking to conceive a child after 35 years of age. It is especially important to get tested for couples who already have a baby with certain disabilities.

Types of diagnostics

There are several ways to test biomaterial for karyotype:

Classic method.
Spectral karyotyping method or SKY method.
Fish or fluorescent hybridization method.

Each of these methods differs not only in the method and approach to research, but also in the collected biomaterial on which testing is carried out to obtain certain results.

In classical testing, blood is taken from a vein (10 to 20 ml). This method has more than 5 varieties. If a diagnosis is made of an already pregnant woman, then, in addition to blood, biomaterial is taken from the amniotic fluid and placenta. In rare cases, the mother's bone marrow cells may be taken for additional diagnostics.

The SKY research method is the latest in the field of genetic diagnostics. Its efficiency is quite high, since it very quickly identifies areas with chromosomal abnormalities. This method is an excellent option when it is impossible to determine abnormalities using the usual karyotyping method. This method is based on staining chromosomes in 24 colors, which makes it possible to determine more complex rearrangements and disorders.

Analysis by the Fish method allows you to identify a large number of diverse abnormalities in chromosomal connections and more complex abnormalities in the karyotype. A feature of the study is a specific approach to certain regions of chromosomes, which are determined by fluorescent tags.

This approach to examination, in contrast to the conventional method, allows us to cover a larger area of the cells being studied for a qualitative characterization of genetic abnormalities. In addition, the analysis is carried out using blood samples and does not require special cell cultivation.

For Fish analysis, biomaterial can be collected from sperm, embryonic or fetal cells. Quite often, for a more accurate picture, specialists, in addition to blood tests, do additional tests to identify chromosomal ailments. If the test result is not very good, then, most likely, the rest of the family members will have to undergo similar studies.

How to prepare for the examination?

The analysis can be prescribed by various specialists involved in family planning and monitoring the couple. But in any case, a competent interpretation of the results will depend on the geneticist. It is best to contact him immediately in the first stages of family planning. Such a doctor will help you correctly assess all existing risks, competently undergo diagnostic tests and choose the optimal solution.

You can take a karyotype test in any convenient and affordable laboratory. These can be either private or public institutions. The analysis is a simple and virtually painless procedure, the principle of which is to donate venous blood. But you should immediately be aware that this type of study lasts a long time, so the results will be available in 2-3 weeks.

Preparation for karyotype analysis is quite simple. It is necessary to stop eating 8-12 hours before collecting biomaterial and it is advisable not to drink 2-3 hours before. There are no special diets or dietary restrictions. You should give up alcohol and cigarettes for a few weeks. It is necessary to stop taking any medications, but if this is not possible, then notify your doctor.

Karyotype analysis can be carried out using various methods. In a normal situation, blood will be drawn; in other cases, according to the doctor’s orders, cellular biomaterial will be taken from various sources.

When patients are undergoing therapy for the treatment of cancer or other diseases with drugs and other methods, it is better not to do a karyotype test. Its results may be distorted due to chromosome damage caused by heavy treatment.

Features of the results

The karyotype of any person has a certain norm. So, men and women must have 46 specific chromosomes. Most often, karyotype studies have a complex meaning. Such a study is especially important after detection of a chromosomal abnormality in the blood. If the examination took place during pregnancy, then additional material will be taken from the placenta to determine possible disorders of intrauterine development of the fetus.

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Deviations from the existing norm can be found in one or both representatives of a married couple.

Therefore, when planning a family, you need to be prepared for the fact that tests, especially of a genetic nature, will need to be taken by both spouses.

Nowadays, genetics has made great strides in diagnosis, so with early detection of abnormalities, the situation can almost always be corrected and prevent repeated miscarriages, unsuccessful conception and other problems. Modern medical capabilities make it possible to correct many situations with chromosomal abnormalities.

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Thanks to the ability to study the karyotype of spouses, it has become quite possible to cure infertility even for those couples who had every reason not to hope for the early appearance of a child in the family.