That's a good question. I can be quite enigmatic at times. Take my name for example: Bleak can be defined as, "offering little or no hope", and an obelisk is a tall, tapering shaft of stone, usually monolithic, of square or rectangle section and ending pyramidally. (i stress the monolithic part)
In short the simplest answer is: I am me.
Kinda lol. Its where you get 3 chromosomes on your 21st Choromosomal pair rather then just 2 chromosomes. and it has a HUGE difference on the human body... not a small one. You won't find someone which a mild case of Down's (lol the only reason i know this is cause we are studying genetics at school)