Several real-world mental disorders are associated with a lack of empathy. The real-world situation informs fiction but neither really mirrors the other. Autistic people and those with Aspergers Syndrome are sometimes held to lack empathy, but it's contended that that they are just bad at expressing empathy. It is also harder for autistic people to tell what someone else is feeling - a problem that easily tips over into a perception of a lack of empathy. In other words, it's not that they don't feel empathy so much as they're bad at perceiving its need and getting others to perceive it in them. This unfortunately contributes to the image of Asperger's Syndrome as being used by people over the Internet as an excuse for being a Jerkass Know-Nothing Know-It-All.