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
Individuals with Down's Syndrome 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 Down's Syndrome results in the over-expression of certain genes, which, in turn, affects their brain and body’s development.
The two most common causes include nondisjunction during meiosis resulting in trisomy 21 (which accounts for the majority of Down’s syndrome cases) and Robertsonian translocation (which accounts for the 2-3% cases).