What Causes Down Syndrome?
Down syndrome results from an error in the genetic development of an embryo. To this day, scientists still do not know why this error occurs, but they do know how. In 1958 two doctors, Lejeune and Jacobs, discovered that Down syndrome was linked to the presence of an extra chromosome (number 21). This breakthrough eventually helped describe the connection between Down syndrome and genes, and why certain characteristics are prevalent in people with the disorder. During the fertilization of an egg under normal circumstances, a zygote is formed that consists of 23 chromosomes each from the egg and the sperm. From this point the new cell – containing 46 chromosomes – will replicate and divide through a process called meiosis. However if either the egg or sperm cell gives an extra chromosome, (chromosome 21) the zygote will end up with 47 chromosomes and the result will be Down syndrome. This is the most common origin of the disorder but not the only way it can occur. There are three different cases in which Down syndrome is the result: Trisomy 21, Mosaicism, and Translocation. The tab labeled Cases explains these cases in more detail. |