Trisomy - what is it, types, causes
Trisomy is the presence of an additional (extra) chromosome in the human karyotype. The violation occurs for very different reasons. Diseases caused by trisomy belong to the category of genetic causes.
Types of trisomies
The most popular types are:
- trisomy on chromosome 21 - Down syndrome;
- trisomy on chromosome 18 - Edwards syndrome;
- trisomy on chromosome 13 - Patau syndrome.
The pathologies listed above are autosomal. Some types of trisomy are considered incompatible with life (the fetus dies in utero at an early stage of its development), they are rather difficult to monitor and investigate, because it is not uncommon for a woman to spontaneously abort with such disorders. The fetus is viable with those trisomies in which additional X and Y (sex) chromosomes are present, such chromosomal disorders often do not manifest themselves clinically throughout a person's life.
Why does trisomy occur
The causes of trisomy are most often hidden in the divergence of homologous chromosomes, as a result of which two chromosomes are found in one cell during division, and none in the other. Non-segregation of chromosomes is detected during oogenesis, similar can be detected during spermatogenesis. This means that the cause of the birth of a child with diseases due to trisomy can be genetic disorders on the part of both the mother and the father.
In any case, the disorder in question is genetic - it cannot be prevented. But modern medicine makes it possible to detect various types of trisomy even at the stage of intrauterine development, which enables parents to make an individual decision about termination of pregnancy or preservation of the fetus, and doctors to prepare for the extraordinary course of pregnancy and childbirth, as well as further monitoring of the child that will be born, and medical appointments
Detection of trisomy
Screening examination of pregnant women is carried out in the first trimester of pregnancy. In order to detect trisomy on chromosome 21, ultrasound is prescribed, and the doctor in the early stages of pregnancy can pay attention to the following factors:
- increasing the collar space;
- lag in the weight and size of the fetus (on average by 8-10%);
- absence of nasal bone.
If two of these disorders are present at the same time, the risk of giving birth to a child with Down syndrome is 40-60%, and future parents must be informed about this.
Additional screenings are mandatory, then the woman is informed of her individual risk of trisomy - not only the ultrasound data, but also the age of the mother/father, order of pregnancy, hereditary factors are taken into account. The risk of having a child with trisomy increases significantly if the pregnant woman is older than 35 years.
Consequences of trisomy
The birth of children with Down's syndrome (trisomy on chromosome 21) is recorded most often, such patients have many developmental pathologies, chronic congenital diseases. They live up to 49 years on average, and some heart defects are treated at an early age by surgical intervention. With a competent approach, patients with Down syndrome can be trained, many of them adapt perfectly in society and lead a fairly active lifestyle.
If a child with Edwards syndrome is born with trisomy on chromosome 18, it is unlikely to live to one year - statistics claim that 90% of newborns with this disease die in the first month after birth. The same applies to Patau syndrome - such a child is extremely rarely born, spontaneous abortion or intrauterine death of the fetus are more common.
You can learn more about X-chromosome trisomy syndrome and how it is diagnosed during pregnancy on our website https://dobrobut.com/.
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