About Down syndrome

Down syndrome was first described medically by an English doctor, John Langdon Down, in 1866 which is where it gets its modern English-language name.
Down syndrome is the most common chromosomal variation in newborn babies. It results from extra genetic material from chromosome 21. In around 95% of cases there is an extra copy of chromosome 21 (trisomy 21). Translocation Down syndrome accounts for about 3% of cases and the least common form of the condition is Mosaic Down syndrome.
Down syndrome is not caused by anything done before or during pregnancy and can occur in any family.
People with Down syndrome do have features in common, but they also closely resemble their parents and family. Many characteristics are attributed to Down syndrome, but any one person will only have some of them. Each person is an individual, with a unique appearance, personality, and set of abilities. The extent to which a child shows the physical characteristics of the syndrome is no indication of their intellectual capacity.