Schizophrenics frequently experience delusions where they believe themselves to be a famous person. Psychosis, the state of being out of touch with reality, is common, as is paranoia, where they believe that they are being observed by some outside force. The features of negative symptoms are blunted or flat effect, where the person's face registers no emotion, avolition, where the schizophrenic has no motivation or initiative, anhedonia, where the schizophrenic cannot experience pleasure and has no interest in life and attention deficits where the schizophrenic is unable to concentrate. In addition, there are several types of schizophrenia. As you can see this is a very complicated disease.
Some doctors think it is a syndrome, or collection of diseases.
It is also speculated that there is more than one gene. Researchers refer to this as polygenic. Perhaps one gene exists for the positive symptoms and one for the negative. To complicate matters further, schizophrenics frequently have other mental disorders such as depression, anxiety disorder and personality disorder. Researchers also feel strongly that the disease has an environmental component.