Causes of Schizophrenia:
Genetics, Environment, and Dopamine

The causes of schizophrenia are unknown: while several possible causes exist, no single cause explains all cases of schizophrenia. Genetics, birth defects, environmental triggers, and imbalances of the neurotransmitter dopamine are all considered possible causes of schizophrenia.

Schizophrenia genetics have been well studied. Studies of identical twins have established that genetics, if not the cause of schizophrenia, at least plays an important role in the development of the illness. If one identical twin develops schizophrenia, the other twin has a forty to fifty percent chance of developing the mental illness.

In addition to twin studies, schizophrenia genetics research has also studied parent/sibling genetics. A person whose parent has schizophrenia has a ten percent chance of inheriting the condition.

Such studies indicate schizophrenia is influenced by genetics, but genetics alone cannot be considered the root cause of schizophrenia. Too many schizophrenia patients have no family history of the illness. Instead, genetics are thought to make certain people more susceptible to schizophrenia. Other considerations, such as environmental factors, may combine with schizophrenia genetics to trigger the disorder.

Dopamine imbalances have been suggested as a possible cause of schizophrenia. Dopamine is a brain neurotransmitter necessary for relaying brain nerve cell impulses. Dopamine's exact role in schizophrenia is unclear. Several arguments can be made in support of high dopamine levels as a cause of schizophrenia:

Antipsychotics and dopamine: Antipsychotic medications, the most common schizophrenia treatment, block dopamine receptors in the brain. By blocking dopamine receptors, antipsychotics limit the amount of dopamine the brain uses.

Illicit drugs and psychosis: Cocaine and amphetamine are both capable of producing psychosis symptoms similar to schizophrenia. Both drugs are also known for their ability to increase dopamine levels.

Proponents of dopamine as a cause of schizophrenia note that the brains of schizophrenia patients have more dopamine receptors than the general population.

Not all schizophrenia researchers are convinced dopamine imbalance is the cause of schizophrenia. Critics of the dopamine theory note that antipsychotic drugs block dopamine levels very quickly, but that schizophrenia symptoms don't improve until after weeks of treatment. Antipsychotics may affect brain chemistry other than dopamine receptors, and improve schizophrenia symptoms in as-yet unknown ways.

Researchers skeptical of the dopamine theory also note new generations of schizophrenia medication block both serotonin and dopamine receptors, and appear to be more effective as treatment for "negative" schizophrenia symptoms. Sypmtoms are divided into two categories: negative and positive. While positive symptoms reflect an excess or distortion of normal functions, negative symptoms are characterized by a loss of normal functions.

Studies of environmental influences on schizophrenia indicate a number of prenatal complications increase the risk of schizophrenia. Rh incompatibility (a blood protein incompatability), maternal influenza infections, and maternal malnutrition are all being investigated as potential sources of increasing the chance of schizophrenia.

Life stressors may trigger schizophrenia in people whose genetics leave them susceptible to the illness. Ending relationships, leaving home, and other life stressors have been linked to schizophrenia onset in some cases.

Certain personality traits, while not causes of schizophrenia themselves, may predispose individuals to the disease. Low levels of social competence and a diminished ability to experience pleasure have been linked to schizophrenia, as have pre-existing problems with cognitive and perception distortion.

Extensive studies have examined the brain structure of schizophrenia patients. Many schizophrenics have enlarged brain ventricles (cavities inside the brain containing cerebrospinal fluid). Some brain regions have been found to be smaller than average. However, not all schizophrenia cases display these brain abnormalities, and many people who do not suffer from schizophrenia have similar brain structures.

Current schizophrenia theories suggest no single cause of schizophrenia exists. Instead, schizophrenia genetics leave some people susceptible to the illness, which is triggered by environmental factors.

It is also worth noting that many schizophrenia experts believe schizophrenia is actually more than one disorder, and that schizophrenia symptoms are actually caused by several subtly different mental disorders. If true, finding a cause for schizophrenia may be extremely complicated: many of the possible theories given above may be true for different varieties of schizophrenia.

Resources

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Chudler, E. (nd). Schizophrenia. University of Washington, Seattle, WA.

Fauci, A., Braunwald, E., Isselbacher, K., Wilson, J., Martin, J., Kasper, D., Hauser, S. & Longo, D. (ed). Harrison's Principles of Internal Medicine, 14th Edition . McGraw-Hill, New York, 1998.

Murphy, M., Cowan, R. & Sederer, L. Blueprints in Psychiatry. Blackwell Publishing, Massachusetts, 2004.

National Institute of Mental Health. (updated 2004). When someone has schizophrenia [NIH Publication No. 01-4599].

National Library of Medicine. (updated 2004). Schizophrenia. MedlinePlus Medical Encyclopedia.

National Mental Health Information Center. (2003, April). Schizophrenia. NMHIC brochure [KEN98-0052].

Spearing, M.K. (2002, August). Schizophrenia [NIH Publication No. 02-3517]. National Institute of Mental Health.