Causes

Abnormal Brain Chemicals. Schizophrenia is associated with an unusual imbalance of neurotransmitters (chemical messengers between nerve cells) and other brain chemicals, such as dopamine overactivity, glutamate, reelin, and others. Whether any changes in these chemicals in the brain is a cause or a consequence of schizophrenia remains unclear.

Abnormal Circuitry. Abnormalities in brain structure are also reflected in the disrupted connections between nerve cells that are observed in schizophrenia. Such miswiring could impair information processing and coordination of mental functions. For example, auditory hallucinations may be due to miswiring in the circuits that govern speech processing. Strong evidence suggests that schizophrenia involves decreased communication between the left and right sides of the brain.

Genetic Factors

Schizophrenia undoubtedly has a genetic component. The risk for inheriting schizophrenia is 10% in those who have one immediate family member with the disease and about 40% if the disease affects both parents or an identical twin. Family members of patients also appear to have higher risks for the specific symptoms (negative or positive) of the relative with schizophrenia.

Researchers are seeking the specific genetic factors that may be responsible for schizophrenia in such cases. Current evidence suggests that there are a multitude of genetic abnormalities involved in schizophrenia, possibly originating from one or two changes in genetic expression. Scientists are beginning to discover the ways in which specific genes affect particular brain functions and cause specific symptoms. Genes that have been studied include the neuregulin-1 gene, the OLIG2 gene, and the COMT gene.

Heredity does not explain all cases of the disease. About 60% of people with schizophrenia have no close relatives with the illness.

Infectious Factors

The case for viruses as a cause of schizophrenia rests mainly on circumstantial evidence, such as living in crowded conditions. The risk is higher for people who are born in cities than in the country. The longer one lives in the city, the higher the risk. The following are some studies suggesting an association:

• Winter and Spring Births. The risk for schizophrenia worldwide is 5 - 8% higher for those born during winter and spring, when colds and viruses are more prevalent.
• Large Families. The risk for schizophrenia is also greater in large families in which there are short intervals between siblings (2 or fewer years). Such observations suggest that exposure to infection early in infancy may help set the stage for later development of the disease.
• Pregnant Mother's Exposure to Viruses. The mother's exposure to viral infections such as rubella, measles, chicken pox, or others while the infant is in the womb has also been associated with a higher risk for schizophrenia in her child.
• Researchers are trying to identify specific viruses that may be responsible for some cases. Of particular interest is research finding evidence of a virus that belongs to the HERV-W retrovirus family in 30% of people with acute schizophrenia.