(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, which is the most common and contributes to 95 percent 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 treatment or prevention.
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.