Genetic Explanation of Schizophrenia
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What are the assumptions of the genetic explanation?
- Schizophrenia is passed on from one generation to the next through our genes
- People are born with an allele predisposing them to schizophrenia symptoms
How are family studies used to support the genetic basis of schizophrenia?
- Schizophrenia tends to run in families
- The closer people are related genetically, the higher the concordance for schizophrenia
What is the risk of schizophrenia in the general population?
What did Kendler et al find in 1985?
First degree relatives of those with schizophrenia were 18 times more at risk of developing the disorder
According to Gottesman and Shields, what is the risk of developing schizophrenia for a person who's parent is schizophrenic?
According to Gottesman and Shields, what is the risk of developing schizophrenia for a person who's sibling is schizophrenic
According to Gottesman and Shields, what is the risk of developing schizophrenia for a sibling with one parent with schizophrenia?
According to Gottesman and Shields, what is the risk of developing schizophrenia for someone with schizophrenic parents?
What can be concluded from Gottesman and Shields' study?
- The more genetically similar someone is with a schizophrenic, the greater the risk of them developing schizophrenia
- If there was no genetic element then there would be no difference in the level of risk between first degree relatives and members of the public
What else could cause the concordance rates to be higher between relatives?
- Family members that are closer genetically are more likely to be brought up in the same environment
- Schizophrenia could be caused by environmental factors instead of genetics
How do Family trees support the genetic explanation?
- They involve the recollection of family members with schizophrenia using a family tree
- Many trees show that schizophrenia clusters in families
- No context into genetic or environmental factors are given
- Schizophrenia diagnosis is historically very inaccurate so relatives could have been misdiagnosed
- Family members might incorrectly identify relatives as schizophrenics
If schizophrenia is purely genetic, what concordance should be expected between monozygotic twins?
- MZ twins share 100% of genes
- The concordance should be 100%
What percentage of genes are shared by dizygotic twins?
What is the average of concordance rates from 5 studies between 1969 and 1976 for Monozygotic twins
What is the average of concordance rates from 5 studies between 1969 and 1976 for dizygotic twins?
What can be concluded from the results of twin studies?
- They suggest there is a genetic link for schizophrenia since the likelihood of developing schizophrenia seems to be linked with genetic relatedness
- if there was no genetic factor there should be no difference between MZ and DZ twins
How can the upbringing of the twins act as a criticism of the genetic theory?
Twins share environment as well as genetics meaning there is no way of telling if the higher concordance is due to environment or schizophrenia
How might the difference in treatment between MZ and DZ twins act as a criticism?
- MZ twins are treated differently that DZ twins with MZ twins treated more similarly, treated as twins rather than individuals and sharing more of the same environment
- The difference in concordance could be caused by greater similarity of upbringing
How might social learning theory explain the fact that MZ twins act more similarly?
- Through vicarious reinforcement
- This could mean that the children are conditioned to display schizophrenic symptoms
How are adoption studies used to support the genetic explanation?
- They separate the environment from the genes
- Children adopted soon after birth don't share the environment of their parents or the genes of their adopted family
What did Heston find in 1966?
- Of 47 mothers with schizophrenia who's children were adopted within days of birth by typical mothers, the instance of schizophrenia was 16%
- This is 16x the average
What did Kety find in 1994?
High rates of schizophrenia were found in people who's biological parents had it but who had been adopted by psychologically healthy parents
What did Tienary find in 1987?
- 155 adopted children with schizophrenic mothers were compared to a matched group with no family history of schizophrenia
- 10% in group 1 were schizophrenic
- 1% in group 2 were schizophrenic
What criticisms can be made about the sample size used in adoption studies?
It is very small and not representative to the entire population so results cannot be generalised
What have further adoption studies found?
- Only children adopted into families with poor communication were at an increased risk of developing schizophrenia
- This suggests that the genetic vulnerability must be triggered by a stressful environment
How can the genetic theory be criticised based on nature/nurture
- It takes an extreme nature or biological stance, ignoring the effect or the environment or nurture
- Many argue that both must be taken into account in order to explain schizophrenia
How is the Genetic theory unethical?
- It is deterministic, stating there is nothing you can do if you are predisposed to the disorder and you cannot really be treated
- This leaves victims with no hope and guilt at passing their genes to offspring
- This leads to the sterilisation and sometimes murder of schizophrenics in eugenics
How is the genetic theory reductionist?
- It reduces a complex disorder such as schizophrenia down to a simple cause- a gene
- This means it ignores other factors such as nurture, learning and the environment
- Schizophrenia is likely caused by an interaction of many factors and the explanation is too simplistic
How is the genetic explanation unfalsifiable and unscientific?
- It is very difficult to identify a particular gene that causes schizophrenia
- Twin and adoption studies are flawed and only lead to correlations
- Schizophrenia is likely cased by multiple genes interacting
What did Myakawa find in 2003?
- DNA of families affected with schizophrenia was studied
- Those with the disorder had a defective gene (PPP3CC), associated with the production of an enzyme
- GMO mice deprived of the enzyme displayed schizophrenic symptoms
How is anthropomorphism an issue with genetic studies?
- A genetic link has been established in mice and rats, not humans
- We are more complex in our cognitions so results collected using animal studies cannot be generalised to the human population
What does the interactionist approach argue?
- People inherit a genetic vulnerability to schizophrenia
- Other factors must be present to trigger the disorder
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