- Down's syndrome
- = Down syndromea condition resulting from a chromosomal abnormality most commonly due to the presence of three copies of chromosome 21 (trisomy 21), which is most likely to occur with advanced maternal age. Down's syndrome can also occur as a result of chromosomal rearrangement (translocation) and as part of a mosaicism, which are not related to maternal age. Affected individuals share certain clinical features, including a characteristic flat facial appearance with slanting eyes (as in Mongolian races, which gave the former name, mongolism, to the condition), broad hands with short fingers and a single crease across the palm, malformed ears, eyes with a speckled iris (Brushfield spots), short stature, and hypotonia. Many individuals also have a degree of mental retardation, although the range of ability is wide and some individuals are of normal intelligence. The incidence of congenital heart defects is 40–50%, and other structural malformations (e.g. duodenal atresia) and associated abnormalities (e.g. deafness, squints, obesity, type 2 diabetes) may also be present.Prenatal diagnosis of Down's syndrome can be obtained by amniocentesis and chorionic villus sampling, which are invasive procedures, and about 33% of structural abnormalities in fetuses with Down's can be detected prenatally by ultrasonography. Prenatal screening tests (e.g. the triple test) and soft ultrasound markers (e.g. nuchal translucency scanning) can estimate the risk of Down's syndrome being present. [L. H. Down (1828–96), British physician]
The new mediacal dictionary. 2014.