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Aetiology
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Dopamine hypothesis
Abnormalities in the dopamine pathways have been implicated as:
- Amphetamines, LSD, bromocriptine and L-dopa can cause schizophrenic like symptoms and are known to enhance dopamine.
- Current anti-schizophrenic drugs are dopamine antagonists and can cause Parkinsonian like symptoms.
- Drugs with geometric isomers are only effective when the isomer is anti-dopaminergic.
- Some limbic pathways that are thought to control mood, behaviour and thought processing utilise dopamine as a neurotransmitter (e.g. mesolimbic, mesocortical).
Neurological dysfunction
- Symptoms similar to schizophrenia are seen in complex partial seizures where left temporal lobe limbic structures are involved e.g. temporal lobe epilepsy.
- Birth complications are associated with an increased risk of schizophrenia suggesting that neurological insults at an early age may play a role in the development of schizophrenia in some individuals.
- The increased rates of winter or spring births (around 10%) found in sufferers may be associated with an increased risk of schizophrenia. The cause, is as yet, unclear but third trimester maternal infection with viruses such as influenza or polio has been postulated.
- Scanning studies in schizophrenics have found smaller structures in the left temporal lobe, ventricular enlargement (correlated with the severity of negative symptoms) and hypofrontality (with functional imaging).
- Movement disorders occur in even unmedicated schizophrenics.
Genetic
The risk for individuals with an affected relative has already been discussed in the section on epidemiology. In addition, since the concordance in twins and other relatives living with a schizophrenic could be attributed to "psychosocial" factors, adoption studies have been carried out. In one study by Heston et al 5 out of 47 children of schizophrenic mothers who were adopted out at birth developed schizophrenia, as opposed to 0 out of 50 controls. In addition around 20% of biological relatives suffered from some form of the disorder, compared to only 6% of adoptive relatives. (These figures became 13% and 1.6% respectively when DSM-III criteria were used).
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