1. Abnormal Cell Division
Down syndrome, a genetic defect that is beyond the control of the parent, occurs when there is an extra copy of the 21st chromosome in all or some of the cells in your body. Chromosomes are structures made from your unique DNA or genetic material, which exist in the nucleus of every cell. Each cell of your body contains 23 pairs of chromosomes or 46 chromosomes all together. In Down syndrome, or Trisomy 21, an error occurs, resulting in an additional copy of the 21st chromosome. This extra genetic material causes the symptoms of Down syndrome.
2. More Chromosomes are Not Better
At conception, part of the genetic material comes from the mother's egg and the other part comes from the father's sperm. The egg and sperm each contain half of the parent's genetic information. In other words, each egg and each sperm contain 23 chromosomes. Occasionally, something goes wrong when the egg or sperm is forming, resulting in an abnormal number of chromosomes. This is what happens with the most common form of Down syndrome. The child inherits an extra copy of chromosome 21 from his mother or father, resulting in 47 chromosomes in each cell of the body.
3. Hidden in the Mosaic
Rarely, Down syndrome results when some of the body's cells contain 46 chromosomes, while other cells contain an extra chromosome. The mixture of normal and abnormal cells creates a mosaic, lending to the name mosaic Down syndrome. Since Mosaic Down syndrome results in both normal and abnormal cells in the body, people can have Mosaic Down syndrome and not show any characteristics of Down syndrome. The extent to which a person is affected depends on the placement of the affected cells in the body and the number of affected cells.
4. Sticky Chromosomes
The last type of Down Syndrome is known as translocation Down Syndrome. This type occurs when a piece of chromosome 21 moves or translocates to another chromosome. The person still maintains two copies of chromosome 21, plus extra bits of chromosome 21 stick to another chromosome, resulting in extra genetic material. This anomaly can occur before or after conception. Translocation Down syndrome is the only form of Down syndrome that may be inherited; however, people with translocation Down syndrome don't always pass it on to their children. Lastly, a person can be a carrier of Translocation Down Syndrome, but not exhibit any characteristics.
5. Age Matters
While there's no reason to believe that any behaviors or environmental toxins contribute to Down syndrome, there is reason to believe that the age of the mother may contribute to the production of an egg with three copies of chromosome 21. This likelihood increases in women over the age of 35. Therefore, doctors recommend prenatal testing, such as amniocentesis, to detect chromosomal abnormalities.
