Schizophrenia, which affects an estimated 3 million people in the United States, is possibly the quintessential mental illness. The stereotypes people have of the mentally ill are symptoms of schizophrenia: disorganized speech reflecting disorganized thoughts, delusions of being persecuted or of being the victim of surveillance, and hallucinations, often of voices issuing disturbing commands. People with schizophrenia are typically socially isolated and unkempt, because the nature of the condition makes it difficult to have normal social interactions or maintain usual standards of dress and hygiene. Additionally, schizophrenia often includes difficulties with what is called "social cognition," meaning the ability to understand and follow the norms of society.
Lately, doctors and researchers have come to regard Schizophrenia as not a single condition but a group of related conditions with overlapping symptoms but different causes and etiologies. All forms generally begin to appear in late adolescence or early adulthood, starting with emotional flatness and social withdrawal. Genetics and environment both are factors in the development of schizophrenia. The roots of the condition appear to lie in the neurotransmitters dopamine and glutamate, along with other chemicals in the brain. Schizophrenic people have different brain structures from people without schizophrenia, but it is not known if the difference is causes schizophrenia or if the disease, along with whatever causes it, itself changes the structure of the brain.
Scientists have revised the estimates of the genetic effect on schizophrenia significantly downward in recent years. One study found that only in 15 percent of genetically identical twins did either both or neither twin exhibit signs of schizophrenia. At any rate, the effect is no more than a greater likelihood of developing the condition. Some people who are genetically prone to the condition seem, for various reasons, to be able to defeat that tendency. High intelligence, which is also the result of a combination of genes and environment, is correlated with a reduced schizophrenia risk; the line between madness and genius may not be as thin and easily crossed as is commonly claimed. It is suggested that environmental factors, such as trauma, that tend to lower intelligence also tend to promote schizophrenia.