At age 18 or so I wrote a scene (opening an otherwise unconceived story) set in the distant future, in which one of the characters was a tiger-striped human. Now . . . Look halfway down this page: Human genetics: Dual identities (Nature, 29 Apr 2002).
2008: The article has vanished. Oh well. It was about mosaicism, and included a picture of a human, apparently the product of two fused embryos, with striped skin.