Down syndrome (Trisomy 21)

Down Syndrome Risk Calculator

Down syndrome is also known as "Trisomy 21" which is a genetic disorder caused by the presence of extra genetic material from part or all of an extra 21st chromosome.  Down syndrome is named after John Langdon Down, the British doctor who described it in 1866. The extra genetic material causes delays in the way a child develops, and often leads to mental retardation. In general,

KaryotypeApproximately one baby out of every 800 has Down syndrome, also known as trisomy 21. A rare opportunity led to the discovery that the chromosome abnormality that causes trisomy 21 seems small but it upsets the entire genome. The lead researcher of the study uses climate change to illustrate the effect.

UltrasoundWomen over the age of 35 are more prone to having children with chromosomal abnormalities such as Down syndrome but, according to the findings of a study presented in February, they are less likely to have a child with anatomi

As many as 60% of a woman's eggs are thought to be defective by errors in chromosomal division. These errors represent the number-one cause of infertility. When conception does occur, these same errors in the chromosomes can lead to Down syndrome and early spontaneous abortion (miscarriage).

Approximately one in every 700 pregnancies in the United States involves an abnormality of the chromosomes, a condition that results in incurable medical conditions such as Down syndrome. Tests for chromosomal abnormalities can be done during pregnancy but they are not always reliable, some come with risk to the pregnancy, and can’t be done until the pregnancy is well advanced.

Down Syndrome (Trisomy 21)

Down syndromeDown syndrome is a genetic disorder caused by a duplication chromosome. Patients with Down syndrome have two copies of chromosome 21 so they are born with 47 chromosomes as opposed to the normal 46. Another name for the condition is Trisomy 21.

Who is at Risk?

down syndrome markersDuring the second trimester, ultrasound can be used to note markers for increased likelihood of Down syndrome, but not all markers are created equal.

Are Chromosomal Disorders Inherited?

Although it is possible to inherit some types of chromosomal abnormalities, most chromosomal disorders (such as Down syndrome and Turner syndrome) are not passed from one generation to the next.

normal karyotypeHuman cells normally contain 23 pairs of chromosomes, for a total of 46 chromosomes in each cell. A change in the number of chromosomes can cause problems with growth, development, and function of the body’s systems.

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