Dictionary > Trisomy 21

Trisomy 21

Definition
noun
A congenital, genetic disorder associated with having an extra copy of Chromosome 21, leading to a set of distinctive physical and mental symptoms, e.g. slanting eyes, broad short skull, broad hands, short fingers, Goldsteins toe sign, and neoteny
Supplement
Trisomy 21 is more commonly known as Down syndrome (or Down’s syndrome. The condition was named after John L. H. Down, a British physician who described it in 1866.
Individuals with Trisomy 21 generally have three copies of Chromosome 21 instead of the normal two. An extra chromosome inside the cells or some of the cells of people with Trisomy 21 results in the over-expression of certain genes, which, in turn, affects their brain and body’s development. Individuals with this type of genetic disorder share common physical features: slanting eyes, broad short skull, broad hands, short fingers, Goldsteins toe sign, and neoteny. Some of the congenital abnormalities associated with trisomy 21 are heart defects, oesophageal atresia and an increased incidence of acute lymphocytic leukaemia.
The two most common causes include nondisjunction during meiosis resulting in trisomy 21 (which accounts for the majority of Trisomy 21 cases) and Robertsonian translocation (which accounts for the 2-3% cases).
Synonym(s):

  • Down syndrome
  • Down’s syndrome
  • mongolism (archaic, offensive)

See also:

  • Aneuploidy
  • Goldsteins toe sign
  • Mongolian fold
  • Nondisjunction


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