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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.
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.
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]
March 21 (3/21) is World Down Syndrome Day, chosen because people with Down Syndrome have three copies of the 21st chromosome instead of the usual two. "Gabe lives his life to the fullest," Nick ...
Brushfield spots are more commonly found in Down syndrome patients of European descent than similarly affected children of Asian heritage. [3] Brushfield spots comprise focal areas of iris stromal hyperplasia, surrounded by relative hypoplasia. Similar spots described by Krückmann [4] and Wolfflin [5] are found in individuals without Down ...
Screening for Down syndrome by a combination of maternal age and thickness of nuchal translucency in the fetus at 11–14 weeks of gestation was introduced in the 1990s. [7] This method identifies about 75% of affected fetuses while screening about 5% of pregnancies. Natural fetal loss after positive diagnosis at 12 weeks is about 30%. [6]