Better known as Down's Syndrome. A congenital abnormality in which the baby is born mentally retarded, with an average IQ of 50 - 60 and with physical deformation of the face (low set ears, sloping forehead, mongoloid eyes), and shortness of stature. Trisomy 21 is caused by an extra chromosome 21 present in the G group. In a small percentage of cases it can be caused by the switching of chromosomes 14 or 15 in the D group or chromosome 21 or 22. Trisomy 21 occurs in about 1 in 650 births, and is more commonly associated with children of mother's over the age of 35. Incidence in children of mothers over the age of 40 can be as high as 1 in 80. Trisomy 21 can be detected prenatally through amniocentesis. The mortality rate is high within the first few years. The disease is also known as mongolism, Down's Syndrome or trisomy G syndrome.
A trisomy for chromosome number 21, or an extra chromosome-21. This is the most common of the trisomies and gives rise to Down syndrome. Research has shown that the commonest source of the extra chromosome is a mistake in the first division of meiosis in the egg cell (during the many years it rests as a primary oocyte).
a genetic disorder in which an individual has an extra 21st chromosome, typically characterized by low muscle tone, cardiac problems, GI malformations, and a distinct facial appearance; also called Down syndrome.