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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.
An anaphase lag of a chromosome 21 in a Down syndrome embryo leads to a fraction of euploid cells (2n cells), phenomenon described as "aneuploidy rescue". There is considerable variability in the fraction of cells with trisomy 21, both as a whole and tissue-by-tissue. This is the cause of 1–2% of the observed Down syndromes. [4]
Mosaic Down syndrome: Only some cells in the person have an extra copy of chromosome 21. This genetic cause is considered rare. This genetic cause is considered rare.
In the United States "special needs" is a legal term applying in foster care, derived from the language in the Adoption and Safe Families Act of 1997. It is a diagnosis used to classify children as needing more services than those children without special needs who are in the foster care system.
The Ts1Cje mouse model of Down Syndrome was developed at the University of California, San Francisco in 1997. This model has a partial triplication of MMU 16 that is smaller than the triplicated region in the Ts65Dn model. Ts1Cje triplication contains what has been identified as the Down Syndrome Critical Region, a region involved in all forms ...
The average IQ of a young adult with Down syndrome is 50, equivalent to the mental age of an 8- or 9-year-old child, but this number varies widely. [3] At the same time, they enjoy a rich social and emotional awareness. [4] Down syndrome is the most common chromosome abnormality in humans, [3] occurring in about one per 1000 babies born each ...
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 exact characteristics of Down syndrome were not observed, so more genes involved for Down syndrome phenotypes have to be located elsewhere. Reeves et al., using 250 clones of chromosome-21 and specific gene markers, were able to map the gene in mutated bacteria. The testing had 99.7% coverage of the gene with 99.9995% accuracy due to ...