Paulie Stewart suffered from one of the many forms of autism spectrum disorder. The cause of this disorder is not known. (A study implicated thiomersol, a mercury-based preservative found in vaccines administered to children, but this has been debunked due to fraud on the part of the original investigator.) Autism is not characterized by any detectable structural brain abnormality. Patients with the disorder range from severe cases, who are all but "locked in" to relatively mild cases who can learn to function if they are careful to avoid certain stressors. Autism is characterized by difficulty in relating to other people; autistic patients do not seem to understand (or understand only with difficulty) the social cues most take for granted. There are indications that autistic patients do not process sensory data in the same way most people do. Some autistics, termed savants, are capable of remarkable feats within a very narrow range of skills. There is presently no cure, but intensive therapy often helps patients improve remarkably.