It is very common in that it occurs in about 1 out of every 100 people. Therefore, twins are not truly identical. The symptoms of schizophrenia fall into two categories, positive and negative symptoms. Some of the positive symptoms are impaired thinking, talking gibberish or to oneself, and experiencing hallucinations of hearing, seeing, smelling, or tasting things that are not present. The schizophrenic might experience command hallucinations which are voices that direct them to harm themselves or others.
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.