According to the CDC, around 6,000 children with Down syndrome are born each year in the USA. Down syndrome is a condition caused by a chromosomal abnormality that alters physical and mental development. People with this condition may have mild to severe cognitive delays. They also typically share physical traits like upward-slanting eyes, small stature and an inability to gain muscle tone, although there are different degrees of severity to these characters. To understand this condition, it's important to know all of the potential causes of Down syndrome and risk factors behind it.
There are three types of Down syndrome, each with separate causes, and trisomy 21 is the most common of these. In trisomy 21, a random error in cell division occurs. This error is called "nondisjunction." Typically, each pair of chromosomes from the father and mother separate at conception, to provide one-half of the embryo's pairs of chromosomes. In trisomy 21, one of the pairs of 21st chromosomes does not separate. As a result, the embryo has three 21st chromosomes instead of two, which is replicated throughout development. This is the most common cause of Down syndrome.
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