Schizophrenia is a mental disorder characterized by delusions, hallucinations and disorganized speech. Genetics play a role in the development of this disorder. According to the "Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition," or DSM-IV, the chance of developing schizophrenia is 10 times greater if you have first-degree biological relatives who have schizophrenia. The presence of certain features in the brain has been associated with schizophrenia. One such indicator is dopamine level.
Dopamine Hypothesis
The dopamine hypothesis is based on a large number of clinical studies. It states that the overproduction of the neurotransmitter dopamine in the brain is common among people with schizophrenia. Therefore, excess dopamine may be the cause of the symptoms of schizophrenia. This hypothesis is the basis for treating people with schizophrenia with medications that block dopamine receptors in the brain.
Twin Studies
Studies involving both monozygotic and dizygotic twins have been conducted to determine the impact of genetics on schizophrenia. Although the dopamine hypothesis has been supported in some cases, the fact that one twin may develop schizophrenia and one may not suggests that environment also plays a role in this disorder. In fact, the chance of identical twins developing schizophrenia is between 30 and 50 percent and the chance for fraternal twins is roughly 15 percent, according to the University of Washington. Therefore, too much dopamine does not necessarily cause schizophrenia.
Parkinson's disease
Side effects of medications for schizophrenia that block dopamine receptors include Parkinson's-like symptoms. This is because Parkinson's disease is the result of low levels of dopamine. However, similar to schizophrenia, Parkinson's disease results in deficits in several areas of functioning, such as cognition, motor skills and memory. In fact, although Parkinson's disease is a movement, not mental, disorder, it has been found to cause dementia in approximately 20 to 60 percent of patients, according to the DSM-IV.
Alternative Hypothesis
Dopamine may not be the only thing to look at when studying brains of people with schizophrenia. As the dopamine hypothesis continues to be studied, some evidence has emerged that glutamate transmission may also play a role this disorder. This alternate hypothesis, described in the "Handbook of Contemporary Neuropharmacology," suggests that a disruption in dopamine transmission may be triggered by a disruption in glutamate transmission. Therefore, the cognitive deficits are caused by the glutamate transmission disruption and the psychotic symptoms are the result of the dopamine disruption.
References
- "Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision"; American Psychiatric Association; 2000
- University of Washington: Schizophrenia
- Schizophrenia.com: Schizophrenia as a Model of Dopamine Disfunction
- "Handbook of Contemporary Neuropharmacology"; Dopamine and Glutamate Hypotheses of Schizophrenia; Bita Moghaddam, Houman Homayoun; March 2007
