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In pregnancies affected by Down syndrome there is a tendency for the levels of human chorionic gonadotropin (hCG) to be increased and pregnancy-associated plasma protein A (PAPP-A) to be decreased. The advantage of nuchal scanning over the previous use of just biochemical blood profiling is mainly the reduction in false positive rates. [11]
If Down syndrome occurs in one in 500 pregnancies with a 90% detection rate and the test used has a 5% false-positive rate, this means, of 20 women who test positive on screening, only one will not have a fetus with Down syndrome confirmed. [114]
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 ...
A study in 2012 found that the maternal plasma cell-free DNA test was also able to detect trisomy 18 (Edwards syndrome) in 100% of the cases (59/59) at a false-positive rate of 0.28%, and trisomy 13 (Patau syndrome) in 91.7% of the cases (11/12) at a false-positive rate of 0.97%.
(MPSS) is estimated to have a sensitivity of between 96 and 100%, and a specificity between 94 and 100% for detecting Down syndrome. It can be performed at 10 weeks of gestational age. [66] One study in the United States estimated a false positive rate of 0.3% and a positive predictive value of 80% when using cffDNA to detect Down syndrome. [67]
Genetics of Down syndrome. Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on chromosome 21, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies greatly from individual to individual, depending on the extent of the extra copy ...
Elevated alpha-fetoprotein refers to a state where alpha-fetoprotein levels are outside of the reference range. There are two categories of AFP tests: tests performed on serum (blood plasma), and tests performed on amniotic fluid. Tests performed on serum are further categorized by the reason for performing the test: maternal serum, adult tumor ...
Down syndrome (DS), caused by trisomy 21, is the most common birth defect associated with intellectual disability. DSCAM plays a crucial role in the development of DS: it is expressed in the developing nervous system, with the highest level of expression occurring in the fetal brain. When over-expressed in the developing fetal central nervous ...