Genetic Explanation of Schizophrenia

• Schizophrenia is passed on from one generation to the next through our genes 
• People are born with an allele predisposing them to schizophrenia symptoms

• Schizophrenia tends to run in families 
• The closer people are related genetically, the higher the concordance for schizophrenia

Around 1%

First degree relatives of those with schizophrenia were 18 times more at risk of developing the disorder

17%

9%

12.9%

46%

• 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

• 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

• 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

• MZ twins share 100% of genes
• The concordance should be 100%

50%

46%

14%

• 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

Twins share environment as well as genetics meaning there is no way of telling if the higher concordance is due to environment or schizophrenia

• 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

• Through vicarious reinforcement 
• This could mean that the children are conditioned to display schizophrenic symptoms

• 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

• 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

High rates of schizophrenia were found in people who's biological parents had it but who had been adopted by psychologically healthy parents

• 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

It is very small and not representative to the entire population so results cannot be generalised

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• People inherit a genetic vulnerability to schizophrenia 
• Other factors must be present to trigger the disorder