Below is the proper use of language for “Down syndrome”:
• Down vs. Down’s - National Down Syndrome Society (NDSS) uses the preferred spelling, Down syndrome,
rather than Down’s syndrome. While Down syndrome is listed in many
dictionaries with both popular spellings (with or without an apostrophe
s), the preferred usage in the United States is Down syndrome. This is
because an “apostrophe s” connotes ownership or possession. Down
syndrome is named for the English physician John Langdon Down, who
characterized the condition, but did not have it. The AP Stylebook
recommends using “Down syndrome,” as well.
• People with Down
syndrome should always be referred to as people first. Instead of “a
Down syndrome child,” it should be “a child with Down syndrome.” Also
avoid “Down’s child” and describing the condition as “Down’s,” as in,
“He has Down’s.”
• Down syndrome is a condition or a syndrome, not a disease.
• People “have” Down syndrome, they do not “suffer from” it and are not “afflicted by” it.
• While it is unfortunately clinically acceptable to say “mental
retardation,” you should use the more socially acceptable “intellectual
disability”. NDSS strongly condemns the use of the word "retarded" in
any derogatory context. Using this word is hurtful and suggests that
people with disabilities are not competent.