(CNN) -- Here's a look at what you need to know about Down syndrome.
Down syndrome is a genetic condition that affects cognitive ability, causing mild to severe learning disabilities and distinctive facial characteristics. There are three types of Down syndrome: translocation, mosaicism and trisomy 21. Trisomy 21 is the most common and contributes to 95% of cases.
Characteristics: English physician John Langdon Down first characterized it in 1866.
It is a condition or syndrome, not a disease.
It is due to extra material in chromosome 21. In those with trisomy 21, the individual possesses a full extra copy of the chromosome.
There is currently no prevention, and treatment includes early intervention, speech, occupational, emotional and other therapies, supplements and drugs and assistive devices.
Risk factors that might lead to the conception of a child with Down syndrome include advanced maternal age or a parent with Down syndrome. A couple that already have a child with Down syndrome has a one percent chance of conceiving another.
The condition can be diagnosed through various prenatal screening tests.
Physical characteristics - small stature, decreased muscle tone, irregular shaped ears, a flat face, eyes that slant upward, a deep crease across the palm of the hands, the ability to extend joints beyond the usual range, a large space between the big toe and the next toe, and a large tongue relative to the mouth size.
Health - Those with the condition may also have, or are at risk for, heart defects, vision and/or hearing impairment, thyroid conditions, obesity, gastrointestinal conditions, memory loss, seizures and some cancers.
Statistics: 3,000 to 5,000 children, or one for every 1,000-1,100 live births worldwide, are born with Down syndrome annually.
250,000 - people in the U.S. have Down syndrome.
One baby in every 830 is born with Down syndrome in the U.S.
Life expectancy is currently 55-60 years.
Language Tips from the National Down Syndrome Society: Down syndrome, without an 's, is the preferred spelling.
"A child/adult with Down syndrome" is the preferred reference, as opposed to "he/she has Down's," or is "afflicted" or "suffers."
The emphasis should be that he/she is a child/adult first, and as a secondary consideration it could be said that the individual has Down syndrome.