There is one disorder I can think of that has a potential upside and that is Geschwind's Syndrome. This is a constellation of personality traits that sometimes accompanies temporal lobe seizures.
One of the traits is called "hypergraphia" and this is the compulsion to write, doodle, make lists, draw - just about anything that can be done with a pencil or pen. The content of the writing is usually philosophical or religious, demonstrating a concern with morality, ethics, the plight of the underdog and the oppressed, and there are frequent digressions into extraneous detail. There is a lot of underlining, capitol letters for emphasis, use of different pen colors, and illustrative doodles and sketches. However, in some people the emphasis is primarily on record keeping in the attempt to make up for the memory problems that seizures cause.
Most people with hypergraphia can't write worth a damn, but they push forward filling up notebook after notebook spurred on by the overwhelming feeling they have something important to say.
In some cases, though, the sufferer actually manages to harness this compulsion to write and doodle and practice it with discipline. Dostoyevski and Lewis Carrol, both diagnosed with epilepsy during their lives, are considered to have written ex epilepsia. Dostoyevsky is classic Geschwinds, and many of Alice's distorted sensory experiences are observed by the neurologically savvy to be among the simple partial seizure symptoms. Van Gogh was also diagnosed as epileptic, and was witnessed having complex partial and grand mal seizures (but for some reason people keep trying to diagnose him with all kinds of other problems). He's an example of someone who channeled his hypergraphia primarily into art: his rate of output was insane, two or three paintings a day, but he also, at the same time, wrote a huge volume of letters to his brother. Author Whitley Streiber is another writer known to have a diagnosis of Temporal Lobe Epilepsy and a lot of people feel his reports of alien abduction are false memories arrived at in recalling snatches of hallucinatory experiences he had during complex partial seizures.
One epileptic I know from an epilepsy forum was employed for years as a newspaper editor, and another had actually written a book that was published. He and his wife managed a motel in Maine and he wrote a book of character studies of some of the stranger guests who'd stayed at the motel. A third guy there wrote crosswords for a London daily paper. Contrast that with a bipolar forum I used to visit. Bipolar people are alleged to be very creative but not one person there ever reported having made any money from writing.
Temporal Lobe Seizures do not make you a good writer, but they do make you an obsessive writer and some manage to hone that urge into good writing.
