Schizophrenia is a mental disorder that makes it difficult to tell the difference between real and unreal experiences, to think logically, to have normal emotional responses, and to behave normally in social situations.

Schizophrenia is a complex illness. Even experts in the field are not sure what causes it. Some doctors think that the brain may not be able to process information correctly.

Genetic factors appear to play a role. People who have family members with schizophrenia may be more likely to get the disease themselves.

Some researchers believe that events in a person's environment may trigger schizophrenia. For example, problems (infection) during development in the mother's womb and at birth may increase the risk for developing schizophrenia later in life.

Psychological and social factors may also affect its development. However, the level of social and family support appears to affect the course of illness and may protect against the condition returning.

There are 5 types of schizophrenia:

• Catatonic
• Disorganized
• Paranoid
• Residual
• Undifferentiated

Schizophrenia usually begins before the age of 45, symptoms last for 6 months or more, and people start to lose their ability to socialize and work.

Schizophrenia is thought to affect about 1% of people worldwide.

Schizophrenia appears to occur in equal rates among men and women, but in women it begins later. For this reason, males tend to account for more than half of patients in services with high numbers of young adults. Although schizophrenia usually begins in young adulthood, there are cases in which the disorder begins later (over 45 years).

Childhood-onset schizophrenia begins after the age of 5 and, in most cases, after normal development. Childhood schizophrenia is rare and can be difficult to tell apart from other developmental disorders of childhood, such as autism.

Schizophrenia may have a variety of symptoms. Usually the illness develops slowly over months or even years.

At first, the symptoms may not be noticeable. For example, you may feel tense, or have trouble sleeping or concentrating. You can become isolated and withdrawn, and have trouble making or keeping friends.

As the illness continues, psychotic symptoms develop:

• An appearance or mood that shows no emotion (flat affect)
• Bizarre motor behavior in which there is less reaction to the environment (catatonic behavior)
• False beliefs or thoughts that have nothing to do with reality (delusions)
• Hearing, seeing, or feeling things that are not there (hallucinations)
• Thoughts "jump" between unrelated topics (disordered thinking)

Symptoms can be different depending on the type of schizophrenia.

Catatonic type:

• Agitation
• Decreased sensitivity to pain
• Inability to take care of personal needs
• Negative feelings
• Motor disturbances
• Rigid muscles
• Stupor

Paranoid type:

• Anger
• Anxiety
• Argumentativeness
• Delusions of persecution or grandeur
• Violence

Disorganized type:

• Child-like (regressive) behavior
• Delusions
• Flat affect
• Hallucinations
• Inappropriate laughter
• Not understandable (incoherence)
• Repetitive behaviors
• Social withdrawal

Undifferentiated type may include symptoms of more than one type of schizophrenia.

Residual type -- symptoms of the illness have gone away, but some features, such as hallucinations and flat affect, may remain.

Because other diseases can cause symptoms of psychosis, psychiatrists should make the final diagnosis. The diagnosis is made based on a thorough interview of the person and family members.

No medical tests for schizophrenia exist. The following factors may suggest a schizophrenia diagnosis, but do not confirm it:

• Course of illness and how long symptoms have lasted
• Changes from level of function before illness
• Developmental background
• Genetic and family history
• Response to medication

CT scans of the head and other imaging techniques may find some changes that occur with schizophrenia and may rule out other disorders.