I'm tring to find a Christmas story I read in an email once. It was about a mother and father whos son was nee

I'm tring to find a Christmas story I read in an email once. It was about a mother and father whos son was needed because his blood type would be able to cure the world of a widespread disease. The story was then linked back to God sending us Jesus Christ as our Lord and Savior. I really love this story. Anyone know of it and where I can find it?