Summary: Mental illness generally doesn't help with creativity. The only thing that correlates is bipolar, and that's only 8% for people entering a creative profession (big Swedish study). However, highly creative people are more likely to have schizophrenic or bipolar first degree relatives.
Research supports the notion that psychologically healthy biological relatives of people with schizophrenia have unusually creative jobs and hobbies and tend to show higher levels of schizotypal personality traits compared to the general population. Note that schizotypy is not schizophrenia. Schizotypy consists of a constellation of personality traits that are evident in some degree in everyone.
Schizotypal traits can be broken down into two types. "Positive" schizotypy includes unusual perceptual experiences, thin mental boundaries between self and other, impulsive nonconformity, and magical beliefs. "Negative" schizotypal traits include cognitive disorganization and physical and social anhedonia (difficulty experiencing pleasure from social interactions and activities that are enjoyable for most people). Daniel Nettle found that people with schizotypy typically resemble schizophrenia patients much more along the positive schizotypal dimensions (such as unusual experiences) compared to the negative schizotypal dimensions (such as lack of affect and volition).
This entry was posted at http://nancylebov.dreamwidth.org/1022198.html. Comments are welcome here or there. comments so far on that entry.