National Insitute of Mental Health: Schizophrenia.
CHRONIC AND SEVERE MENTAL DISORDER AFFECTING HOW A PERSON THINKS, FEELS, AND BEHAVES
Schizophrenia is a severe brain disorder. People who have it may seem like they have lost touch with reality and hear voices, see things that aren't there or believe that others are reading or controlling their minds. Symptoms usually start between ages 16 and 30, but children can also show signs and symptoms. They include hallucinations and delusions such as hearing voices. Other symptoms include:
• Unusual thoughts or perceptions
• Agitated body movements
• Difficulty speaking and expressing emotion
• Reduced facial expressions and tone of voice known as "flat affect"
Scientists believe that genetic makeup and brain chemistry play a role at increasing the risk of Schizophrenia. Scientists also believe that a combination of genes and environmental factors increase your risk, including exposure to viruses, malnutrition before birth, or problems during birth.