Extrasensory Perception, or ESP, is more of an ability than it is a mental condition-- however, since it is an abnormal quality, it qualifies as a disease. This does not mean characters with ESP are mentally challenged in any fashion. It just means their minds function slightly differently than everybody else's, and that's not necessarily a bad thing!
There are two branches to ESP.
Psychological ESP Edit
Psychological ESP, or Ps.ESP, includes the ability to read minds. While it can be a useful tactic,it could easily be the heartbreaking downfall of a character, especially if they are impulsive. Acting upon others' thoughts isn't a healthy way to get around, as it can be quite creepy. It can make others self-conscious, or even angry... It's almost as if nobody's allowed to think around these kinds of characters!
Physical ESP Edit
Physical ESP, or Ph.ESP, allows characters to feel what others can without experiencing it themselves. To some, this is a natural process. To others, they can become mentally attached to somebody to the point to where they're practically one person. Again, this can be quite creepy, as the character[s] with this form of ESP could react spontaneously to whatever happens to the one[s] they are bonded with.