Many children with chromosomal problems have mental and/or physical birth defects. Some chromosomal problems eventually lead to miscarriage or stillbirth.
Chromosomes are thread-like structures that are located in the cells of our body and contain a set of genes. In humans, there are about 20–25 thousand genes that determine such signs as eye and hair color and are also responsible for the growth and development of each part of the body. Each person has a normal 46 chromosomes, assembled into 23 chromosomal pairs, in which one chromosome is inherited from the mother and the second from the father.
Causes of chromosomal abnormalities
Chromosomal pathologies are usually the result of an error that occurs during the maturation of the sperm or egg. Why these errors occur is not yet known.
Oocytes and spermatozoa normally contain 23 chromosomes each. When they join, they form a fertilized egg with 46 chromosomes. But sometimes something goes wrong during (or before) fertilization. For example, an egg cell or a sperm cell may develop incorrectly, as a result of which there may be extra chromosomes, or, conversely, there may be a lack of chromosomes.
At the same time, cells with the wrong number of chromosomes join a normal egg cell or a sperm cell, as a result of which the resulting embryo has chromosomal abnormalities.
The most common type of chromosomal abnormality is called trisomy. This means that instead of two copies of a particular chromosome, a person has three copies. For example, people with Down syndrome have three copies of chromosome 21.
In most cases, an embryo with the wrong number of chromosomes does not survive. In such cases, the woman has a miscarriage, usually in the early stages. This often happens at the very beginning of a pregnancy, before a woman can understand that she is pregnant. More than 50% of miscarriages in the first trimester are caused by chromosomal abnormalities in the embryo.
Other errors may occur before fertilization. They can lead to a change in the structure of one or more chromosomes. In people with structural chromosomal abnormalities, as a rule, the normal number of chromosomes. However, small pieces of the chromosome (or the entire chromosome) can be deleted, copied, inverted, inappropriate, or can be exchanged with part of another chromosome. These structural adjustments may not have any effect on a person if he has all the chromosomes, but they are simply rearranged. In other cases, such rearrangements can lead to a pregnancy loss or birth defects.
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