What causes Down syndrome during pregnancy?

(June 26, 2010)

Pregnancy Down Syndrome

Down syndrome (DS) is a genetic disorder that results in a delay in the child’s development; the delay can affect both mental and physical development, often resulting in mental retardation or physical defects.  DS is caused by the presence of an extra chromosome, chromosome 21, and hence, DS is also known as Trisomy 21.

The nucleus of each cell in the human body stores the genetic imprints or codes, simply put, the genes. Normally, each cell and each sperm contains 23 chromosomes. The union of an egg and sperm results in 23 pairs of chromosomes, i.e., 46 chromosomes. In DS, due to an error in cell division, known as non-disjunction, the child has three copies of chromosome 21 instead of the usual two. As the embryo develops, this chromosome is replicated in each cell of the body. Apart from non-disjunction, DS can also manifest as a result of mosaicism and translocation.  

In translocation, the extra long part of chromosome 21 breaks off during cell division and attaches itself to another chromosome. Thus, while these are a total 46 chromosomes, the presence of an extra part of chromosome 21 result in the characteristics of DS. Mosaicism occurs when non-disjunction takes place in one cell and not all the cells of the body. When this happens, there are different types of cells, those containing 46 chromosomes and those containing 47 chromosomes.
Typically, DS results in mild to moderate mental or physical retardation. Most babies that have DS also have problems related to the heart, intestines, and thyroid. Such babies also have hearing loss and vision trouble. While most of the problems can be treated with medical and educational assistance, surgery may be required in a few cases.

There are various prenatal screenings and diagnostic tests that can be done during the pregnancy to detect the chances of the infant having DS. In the screening tests, the mother’s blood is examined to determine if there is increased risk of DS. It should be noted that although these tests are simple and noninvasive, they are slightly risky as they can increase the chances of a miscarriage. If the pre-diagnostic tests reveal that the baby has DS, you can mentally, emotionally and medically prepare yourself for the delivery. Keep in mind that there is no cure for DS nor is there any preventive measure against the chromosomal abnormality.

Lastly, research has shown that DS is more common in children born of older mothers, women above the age of 30. However, this is not to say that children born of women over the age of 30 will have DS.

Submitted by N H on June 26, 2010 at 07:06

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