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Schizophrenia: Overview and Risk Factors

Schizophrenia is characterized by the presence of delusions and/or hallucinations, as well as disorganized speech and behavior. It is also marked by the loss of normal functions, particularly emotional expression, productivity of thought and speech, and goal-directed behavior. Although it is discussed here as a single entity, schizophrenia is likely composed of a group of disorders that are heterogenous in origin, despite similar symptomatology. An excess of brain dopamine activity is presumed to underlie these symptoms, but its etiology is likely multifactorial and remains an area of ongoing research.

The disorder affects about 1% of people worldwide. Schizophrenia occurs in people of all social classes, although patients are often socially and economically marginalized as a result of the disease and its accompanying stigma, resulting in lowered socioeconomic status.

Risk Factors

Age. The onset of schizophrenia is typically before age 35, and the illness persists throughout life. Although the lifetime risk for men and women is similar, onset is often later in women than in men, with a second peak onset around menopause, suggesting a protective role for estrogen. Peak onset for men is age 10-25, and for women is age 25-35. Less than 10% of women present after age 40 (usually perimenopausally).

Genetic Factors. Approximately half of monozygotic twins are affected when the other twin has schizophrenia. The risk to dizygotic twins is around 15%, and first-degree relatives have about a 10% risk. However, no specific gene has been isolated, and several genes may play a role.

Early Developmental Influences. Analgesic use during the second trimester1 or hypertension and diuretic use during the third trimester of pregnancy may be associated with increased risk of schizophrenia for the newborn.2 Fetal malnutrition, paternal age over 50 years,3 and winter/spring births (presumably related to viral infections) are also associated with increased risk. Persons who were not breast-fed for at least 2 weeks have been shown to have increased prevalence of schizophrenia,4 and a child with a genetic predisposition to schizophrenia may have a further increased risk if a childhood head injury occurs.

Toxoplasma gondii. This organism may infect the central nervous system and may be associated with schizophrenia.


Schizophrenia: Diagnosis and Treatment >>