DescriptionAn in-depth report on the causes, diagnosis, and treatment of schizophrenia
No single cause can account for all cases of schizophrenia. Rather, it appears to be the result of multiple "hits" from genetic factors, environmental and psychological assaults, and possible hormonal changes that alter the brain's chemistry and trigger this devastating disease.
Abnormalities in Brain Structure, Circuitry, and Chemicals
Brain scans using magnetic resonance imaging (MRI) have now detected a number of abnormalities in the brain's structure that have been associated with schizophrenia. Such abnormalities can cause nerve damage and disconnections in the pathways that carry brain chemicals.
Abnormalities of Brain Volume and Activity. Imaging techniques have revealed reduced volume and actual loss of tissue in the brains of people with schizophrenia. Of particular importance are volume losses and abnormal activity in the prefrontal cortex, which contains the white matter of the brain, and the temporal lobes, which contain the limbic system.
Abnormal Brain Chemicals. Schizophrenia is associated with an unusual imbalance of neurotransmitters (chemical messengers between nerve cells) and other factors.
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.
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 (i.e., 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.
An international team has identified the neuregulin-1 gene as a major candidate gene for schizophrenia risk. This gene is involved with growth of the glial cells in the brain, memory, and motor neuron functioning, all of which are abnormal in schizophrenia.
Other research targets are genes that affect brain structure. For example, mutations in the COMT gene may make people susceptible to deficits in the prefrontal cortex of the brain, where schizophrenia develops. In addition to COMT and neuregulin-1, other genes and genetic regions implicated in schizophrenia include dysbindin, G72, RGS4, PPP3CC, and others.
It should be noted that heredity does not explain all cases of the disease. About 60% of people with schizophrenia have no close relatives with the illness.
Viruses. The case for viruses as a cause of this disease rests mainly on circumstantial evidence, such as living in crowded conditions. The following are some studies suggesting an association:
Toxoplasmosis. Some researchers have found an association between some cases of schizophrenia and toxoplasmosis (a parasite carried by cats and other domestic animals), which can lie dormant in the nervous system and migrate to the brain over many years. Schizophrenic patients who are exposed to the parasite respond poorly to clozapine treatment. There is no evidence, however, that exposure to toxoplasmosis causes schizophrenia.
Loss of Oxygen around the Time of Birth
Many studies have reported an association between schizophrenia and problems surrounding birth, particularly those that cause oxygen deprivation, which could affect the nerve growth or structure in the developing brain. Specific complications that have been associated with such a higher risk include the following:
Although parental influence is no longer believed to play a major role in the development of schizophrenia, it would be irresponsible to ignore outside pressures and influences that may exacerbate or trigger symptoms. The prefrontal lobes of the brain, which are the brain areas often thought to lead to this disease, are extremely responsive to environmental stress. Given the fact that schizophrenic symptoms naturally elicit negative responses from the sufferer's circle of family and acquaintances, it is safe to assume that negative feedback can intensify deficits in a vulnerable brain and perhaps even trigger and exacerbate existing symptoms.
One study to support this indicated that early parental loss, either from death or separation, increases the risk for psychiatric disorders, including schizophrenia. In another interesting 2000 study, criticism by family members was significantly correlated with the onset of disorganized thinking in patients with impaired working memory. (This effect of criticism was not observed in patients with functioning working memories.)