Overview of Down syndrome (Trisomy 21)

Humans have 23 pairs (46) chromosomes due to genetic characteristics. The condition that chromosome number 21 is double, that is, not two, but three is called Down syndrome. There are 47 chromosomes in total.

On average, there is a risk of developing Down syndrome in every 800 births. The risk increases in pregnancies over the age of 35.

Down syndrome has a unique facial structure. There is moderate or mild mental development disorder.

Types of Down Syndrome:

There are three different types of Down syndrome. These:

• Trisomy 21: It is the most common (95%) type. The 21st chromosome is an excess as a result of incorrect division.
• Translocation: It is seen in a few (2-3%). As a result of a break in the 21st chromosome, a piece breaks off and attaches to another chromosome. Although a person has 46 chromosomes, he has 47 chromosome information.
• Mosaic: It is seen rarely (1-2%). Some body cells have an excess of 21st chromosomes, while others do not.

Risk Factors for Down Syndrome:

Every pregnancy has a risk of developing Down Syndrome. However, some factors increase this risk. These:

• Maternal age: The majority of Down syndrome cases occur in pregnancies under 30 years of age. This is due to the fact that there are many more births in this period and it is proportionally lower than the older age groups. Pregnancy over the age of 35 has a much higher risk of Down syndrome.
• Week of pregnancy: The risk of Down syndrome is higher in the first months of pregnancy and less in the following months.
• History of baby with chromosomal abnormality: Pregnant women who have given birth to a baby with chromosomal abnormality in their previous births have a higher risk of giving birth to Down syndrome.

Prenatal screening:

Different tests can be done to investigate the presence of Down Syndrome in the fetus before birth. These:

• Alphafetoprotein level : Alphafetoprotein is the main protein of the fetus and its level increases as the gestational week increases. This level is low in Down syndrome.
• Triple Screening Test : It is the most widely used test. 15-21 days of pregnancy. done during the week. HCG, alphafetoprotein and E3 levels are checked.
• Ultrasonography: Ultrasonographic examination performed in the second trimester of pregnancy is also diagnostic of increased nuchal edema, nasal bone problems and other anomalies in the fetus. It can also be useful in the detection of other congenital diseases.