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.
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.
Statistics
Language Tips from the National Down Syndrome Society
“A child/adult with Down syndrome” is the preferred reference, as opposed to “he/she has Down’s,” or is “afflicted” or “suffers.”