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Down syndrome or Down's syndrome, [12] also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. [3] It is usually associated with developmental delays, mild to moderate intellectual disability , and characteristic physical features.
The second, combined with a normal gamete from the other parent, gives rise to a typical child. The third leads to a translocation Down syndrome child. The last becomes a translocation carrier, like the parent. Translocation Down syndrome is often referred to as familial Down syndrome. It is the cause of about 4.5% of the observed Down ...
Down syndrome is usually diagnosed during pregnancy through genetic screening or at birth through diagnostic tests. There are some distinct physical features that typically occur in individuals ...
In fact, consider that Down syndrome affects about 1:400 pregnancies; if you screened 4000 pregnancies with a Quad test, there would probably be 10 Down syndrome pregnancies of which the Quad test, with its 80% sensitivity, would call 8 of them high-risk. The quad test would also tell 5% (~200) of the 3990 normal women that they are high-risk.
Some parents opt for prenatal screenings or diagnostic tests to understand their baby’s risk of Down syndrome. Here’s what to know about the different types of Down syndrome tests and their ...
Karyotype of a human with Trisomy 21 (Down syndrome). Trisomies can occur with any chromosome, but often result in miscarriage rather than live birth.For example, Trisomy 16 is most common in human pregnancies, occurring in more than 1%, but the only surviving embryos are those having some normal cells in addition to the trisomic cells (mosaic trisomy 16). [3]
The most common abnormality the test can screen is trisomy 21 (Down syndrome).In addition to Down syndrome, the triple and quadruple screens assess risk for fetal trisomy 18 also known as Edwards syndrome, open neural tube defects, and may also detect an increased risk of Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith–Lemli–Opitz syndrome, and steroid sulfatase ...
The genetics and abortion issue is an extension of the abortion debate and the disability rights movement.Since the advent of forms of prenatal diagnosis, such as amniocentesis and ultrasound, it has become possible to detect the presence of congenital disorders in the fetus before birth.