2. Down syndrome is a Trisomy - meaning there are 3 copies, instead of 2, of any given chromosome. Medically Down syndrome is known as Trisomy 21 because it's the 21st chromosome that is affected; it's also the most common type of trisomy. Down syndrome is not a disease.
3. There are 3 types of Down syndrome - the most common (about 95% of cases) is nondisjunction which is a 3rd copy of the chromosome in every cell.
Mosaicism (about 1-2%) happens when only some of the cells have the extra 3rd copy.
Translocation (about 2-3%) happens when the long arm of chromosome 21 is attached to another chromosome.
4. In the US, Canada, and some other countries, it is Down syndrome, not the possessive "Down's syndrome." (The UK is one country still using the possessive form.) In 1975, the United States National Institutes of Health convened a conference to standardize the nomenclature of malformations. They recommended eliminating the possessive form: “The possessive use of an eponym should be discontinued, since the author neither had nor owned the disorder.” John Langdon Down first described it in 1866, but he neither had it, nor "owned" the syndrome so it should not take on the possessive form of Down's syndrome. (An example of possessiveness is ALS is also known as Lou Gehrig's disease, because he had the disease.) The 2 other common trisomies are 18 and 13, also known as Edwards syndrome and Patau syndrome - notice no possessive form on those syndromes.
5. While Dr. John Langdon Down first described the common characteristics of people with Down syndrome, it was actually Dr Jerome Lejeune who first identified it as a chromosome 21 trisomy in 1959.
6. While the likelihood of giving birth to a child with Down syndrome increases with maternal age; nevertheless, 80% of babies with Down syndrome are born to women under 35 years of age, as women in that age group give birth to more babies overall.
7. Down syndrome is not related to race, nationality, religion or socio-economic status.
8. Down syndrome occurs in about 1 in 800 live births.
9. There is a wide variation in mental abilities, behavior and physical development in individuals with Down syndrome. Each individual has his/her own unique personality, capabilities and talents. In other words, people with Down syndrome are not all the same; just like individuals in the typical population are not all the same.
10. Life expectancy for people with Down syndrome has increased dramatically in recent decades - from 25 in 1983 to 56 today.