A new model of mental illness proposes that schizophrenia, like other mental illnesses, has no single cause. Rather, it is believed to be the result of a combination of psychological, biological (including genetic), and social factors interacting to produce disease. This is called the bio-psycho-social model of mental illness.
Although schizophrenia occurs in one percent of the general population, its incidence among people with at least one first-degree relative (father, mother, brother, or sister) is as high as 10 percent. This indicates there is a genetic component to the disease.
The incidence of schizophrenic disorders among second-degree relatives (uncles, cousins, grandparents, etc.) is also higher than among the general public. Although this also suggests a genetic cause, experts believe that numerous genes may be involved; schizophrenics tend to have a greater degree of genetic mutations in general than healthy people. At least one of these genetic abnormalities is thought to affect the development of brain chemicals called neurotransmitters, while other gene mutations may affect brain development.
Although some of the genetic abnormalities associated with schizophrenia have been identified, it is not presently possible to predict who will develop the disease based on analysis of individuals’ genomes. Scientists suspect that schizophrenia develops only after certain environmental factors have interacted in some way with one or more of these genetic mutations. Thus, the “nature versus nurture” (genetic makeup versus environmental influences) argument may be moot. In this more likely scenario, both nature and nurture play a role in the development of the disease.
Environmental and Biological Triggers
Hypothesized triggers include maternal exposure to a virus (including rubella, poliovirus, respiratory viruses, etc.), malnutrition of the mother during pregnancy, and difficulties during labor and delivery. Recent evidence suggests that inflammation may play a role in schizophrenia, although the exact relationship between the two conditions remains unclear. Emerging information indicates that people with schizophrenia and other neuropsychiatric disorders often have higher than normal blood levels of proteins involved in inflammation. In fact, it has been suggested that common antidepressant and antipsychotic medications relieve symptoms, at least in part, by modulating inflammation.