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(CNN) Here's a look at Down syndrome, 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.
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 has 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 - People with Down syndrome 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.
In the United States, about 6,000 children are born with Down syndrome annually.
In 2008, about 250,000 people in the United States were estimated to have Down syndrome.
The average life expectancy is about 60 years.
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."