If you get a chance, read this week's Annals of Medicine article entitled "An Error In the Code". It doesn't appear to be online, but if you have the magazine, don't miss this article. It's about a very rare disorder called Lesch-Nyhan. I really can't say anymore because it's almost impossible to describe this syndrome, but the story really made me appreciative of what I've got.
Here's a little bit on the syndrome: http://www.ninds.nih.gov/disorders/lesch_nyhan/lesch_nyhan.htm