Biological explanations of schizophrenia

Biological explanations of schizphrenia for AQA. Includes genetic factors, dopamine hypothesis, evolutionary etc.

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  • Created on: 11-06-12 12:58
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Biological explanations of schizophrenia
Genetic factors
Family Studies
Gottesman (1991) found that schizophrenia is more common in people who are genetically related.
The closer the relationship the higher the risk.
Someone who has two schizophrenic parents has a CR of 46% could be the environment that they
learn the behaviour from copy parent behaviour and think that it is normal.
Someone who has one schizophrenic parent has a CR of 13%.
Comparing 46% with 13% the behaviour could be copied because they have one normal parent.
Someone who had a schizophrenic sibling has a CR of 9%.
However the fact that it runs in families could be due to rearing practices.
Twin studies
MZ twins share 100% genes DZ twins share 50% genes.
If MZ twins are more concordant it suggests this is due to genetics.
Joseph (2004) did a metaanalysis polled the data for all twin studies done before 2001 and found
CR for MZ twins was 40% and 7% for DZ. It is widely accepted that MZ twins are treated more
similarly and the difference in concordance rate is likely to be due to environmental factors rather
than genetics.
Can't just be due to genes, must be environmental factors as well, otherwise it would be 100%.
However more recent studies use better methods where the assessors of the twins don't know
which is MZ and which is DZ this removes the experimenter bias and leads to more valid results.
CR for MZ is lower than 40% but still higher than DZ.
Adoption studies
Adoption studies try to separate out genes and environment.
Tienari et al. (2000) studied 164 adoptees with schizophrenic biological mothers and 6.7% of the
adoptees had schizophrenia.
Of the 197 control only 2% had schizophrenia.
If one parent has schizophrenia the CR is 13% but adoptees have a CR of 6.7% with a
schizophrenic biological mother therefore suggesting that the environment plays an important
Joseph (2004) claims that in countries such as Denmark and the US, potential adoptive parents
who would have been informed of the genetic background of children before the selection for
As Kringlen (1987, cited in Joseph, 2004) points out `because an adoptive parent evidently received
information about the child's biological parents, one might wonder who would adopt such a child'.
The dopamine hypothesis
Dopamine is a neurotransmitter that operates in the brain. The dopamine hypothesis states that messages
from neurons that transmit dopamine fire too easily or too often leading to the characteristic symptoms of
schizophrenia. Schizophrenics have too many D2 receptors on the receiving neuron and this results in more
dopamine binding to the neuron and therefore more neurons firing. (Comer, 2003) found that access
dopamine causes problems relating to attention, perception, thought and emotion.

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Amphetamines are a drug with special relevance for understanding schizophrenia. It is a dopamine
agonist stimulating nerve cells containing dopamine causing the synapse to be flooded with this
Large doses of the drug can cause the hallucinations and delusions of a schizophrenic episode.
Antipsychotic drugs
There are many types of antipsychotics, but they all block the activity of dopamine in the brain. It
reduces stimulation of dopamine in the brain and eliminates symptoms, such as hallucinations
and delusions.…read more


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