Down syndrome: causes, signs and prenatal diagnostics
Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21. Human cells normally have 46 chromosomes (23 pairs), but in Down syndrome, an extra chromosome 21 is present, bringing the total number of chromosomes to 47.
Table of Contents
Down syndrome is not a disease—it is Genetic condition, which affects a person's physical development, learning characteristics, and certain aspects of health. Each person with Down syndrome is an individual and developmental opportunities vary significantly.
Why does Down syndrome develop?
The exact cause of Down syndrome is not always known. Most often, it develops as a result of a random genetic change when chromosomes do not divide correctly during the formation of an egg or sperm.
A baby with Down syndrome can be born at any age, although the likelihood of developing the condition increases as a woman ages. However, the majority of babies with Down syndrome are born to relatively young women because the overall number of pregnancies in this age group is high.
Main features
Down syndrome may be accompanied by certain physical signs and health characteristics, although their manifestation is not the same in every person.
Possible physical signs include:
- Characteristic facial features;
- Low muscle tone (hypotonia);
- Features of the structure of the hand and fingers;
- Certain features of the structure of the eye;
- Relatively short neck;
- Growth and development characteristics.
People with Down syndrome sometimes have a higher risk of developing certain co-occurring health problems, including:
- Congenital heart defects;
- Vision and hearing impairments;
- Changes in thyroid function;
- Gastrointestinal system problems;
- Some blood diseases, including certain forms of childhood leukemia.
Regular medical monitoring and timely examinations help in the early detection and management of potential problems.
Genetic forms of the condition
There are several genetic forms of Down syndrome:
Trisomy 21 — The most common form, accounting for about 95% of cases. In this case, there is an extra 21st chromosome in all cells of the body.
Translocation form — Occurs in approximately 3–4% of cases and is associated with the attachment of part of chromosome 21 to another chromosome.
Mosaicism — A rare form (about 1–2%) in which some cells in the body contain 46 chromosomes and some contain 47.
Prenatal diagnostics
Two main approaches are used to assess chromosomal abnormalities in the fetus during pregnancy:
1. Prenatal screening tests
Screening studies assess how high or low the probability of a fetus having certain genetic conditions is.
They include:
- First trimester screening (ultrasound examination and maternal blood biochemical markers);
- Non-invasive prenatal testing (NIPT) — Fetal-free DNA (cfDNA) testing in maternal blood.
NIPT is a highly accurate screening method that is particularly effective for assessing the risk of Down syndrome.
2. Diagnostic tests
If the screening result indicates a high risk of a chromosomal abnormality, your doctor may recommend diagnostic testing.
Diagnostic methods directly examine the genetic material of the fetus and include:
- Chorionic villus sampling (CVS);
- Amniocentesis.
These studies provide an accurate answer, although they are associated with small risks to pregnancy due to their invasiveness.
How to support
Down syndrome is a lifelong genetic condition, but with the right support and early intervention, people can develop important skills and reach their full potential.
Early development programs may include:
- Speech therapy;
- Physical and occupational therapy;
- Educational support.
The modern approach involves not only medical supervision, but also the creation of an environment that promotes the full integration and development of abilities of people with Down syndrome.
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