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Schizophrenia is not attributable to one cause. Rather, it appears to result from a combination of genetic and environmental factors.

Genetic Factors

Although only 1% of the population develops schizophrenia, the following patterns have been noted in families:

• According to the American Psychiatric Association (APA), the risk of developing schizophrenia for a child with one parent who has the condition is 13%. If both parents have schizophrenia, the risk of a child developing the condition is 35-40%. The risk rises with increasing numbers of affected first or second-degree relatives.
• Second-degree relatives, (aunt, uncle, cousins, and grandparents) develop schizophrenia at a rate higher than the general population but lower than first-degree relatives. An identical twin of a person with schizophrenia has a 60-84% chance of developing the condition.

Research indicates that there are several genes involved with increasing the risk of schizophrenia but that each individual gene has a small effect and cannot cause schizophrenia by itself. When these genes act together with biological and environmental factors, clinical schizophrenia develops.

Environmental Factors

Environmental factors include:

Biological factors

• Viral infections
• Pregnancy-related events such as maternal flu, rubella, diabetes, smoking, or fetal malnutrition
• Birth-related difficulties, particularly any situation causing hypoxia (temporary oxygen deprivation) of the baby, or low birth weight
• Season of birth - rates of schizophrenia are higher in babies born in the winter of each hemisphere (between January and April in the Northern hemisphere and between July and September in the Southern hemisphere)

Psychosocial factors

• Poverty
• Lower social class
• Born in urban (rather than rural) areas
• Stressful home life or other highly stressful situations or events
• Drug abuse

Scientists continue to investigate the pathophysiology of schizophrenia where research has indicated:

• An imbalance of chemical reactions involving the neurotransmitters dopamine, glutamate, and possibly others as well
• Positron Emission Tomography (PET scans) imaging studies indicate abnormal blood flow in some regions of the brain in schizophrenic patients while they are performing tasks involving executive functioning (problem solving) and other cognitive functions.
• Schizophrenic patients lack glial cells which are markers of brain injury or neurodegenerative disorders, indicating that these structural changes occurred early in neural development and not after birth.
• Enlarged ventricles and other structural changes in the brain of some patients with schizophrenia
• Reduction in volume of brain tissue in some schizophrenic patients

The last two observations are found not only in many newly diagnosed patients, but also in relatives who are at high risk of developing schizophrenia. These findings as well as others are leading scientists to believe that schizophrenia is related to abnormal structural changes in the brain that take place early in brain development, indicating the involvement of impaired genetic programming in the fetus.

Imaging studies in schizophrenia is an active area of research as scientists seek to learn more about brain anatomy and function in patients with the condition.

Based on all of this research and more, one of the prevailing theories regarding the etiology of schizophrenia is called the Vulnerability/Stress Model which proposes that abnormal brain development as a result of genetic predisposition or adverse effects during pregnancy and delivery set the foundation for increased risk for vulnerability in developing schizophrenia.