Biological Explanations for Schizophrenia
Revision note: There are similarities between biological explanations for schizophrenia and the
three biological explanations for aggression: genetics, neurotransmitter activity and structural
defects.
Genetics
- Unlike aggression (MAOA-L) and OCD (COMT/SERT) there is no single gene that is linked to
schizophrenia. Instead, there are many candidate gene combinations. Therefore,
schizophrenia is polygenic – Ripke argues there are 108 gene combinations – makes
people more vulnerable
- The genetics explanation for schizophrenia overlaps with the genetic explanation for aggression. The
A01 is similar as the same methodology is used: twin studies, family studies and adoption
studies.
- This therefore means that the A03 also overlaps with the genetic explanations for aggression too as
you can cover the same methodology problems – for e.g. MZ twins may have higher concordance
rates than DZ twins, but this isn’t necessarily due to greater genetic similarity, it could be that MZ
twins are treated more similarly than DZ twins and therefore the higher concordance rate is
produced by a more similar environment
(Discuss this in A01):
Type of method How it works What it should show if schizophrenia
is genetic
Twin study Compare the concordance rates of If schizophrenia is genetic, MZ twins should
the MZ (monozygotic/identical) twins have a higher concordance rate than DZ
who share 100% of their genes with twins
DZ (dizygotic/non-identical) twins
who share 50% of their genes
Family study Identify families who have a family The risk of developing schizophrenia
member with schizophrenia. increases with genetic relatedness / the
Compare the risk of developing closer your relationship to a family member
schizophrenia for their relatives, with schizophrenia, the greater the chance
based on how closely of you developing schizophrenia
related/genetically similar they are
Adoption study Compare adopted children who Adopted children who have a biological
have a biological parent with parent with schizophrenia are more likely
schizophrenia to a control group of to develop schizophrenia than a control
adopted children who don’t have a group of adopted children who don’t have a
biological parent with schizophrenia. biological parent with schizophrenia
(Discuss this in A03):
(Twin studies) Joseph (2004) calculated that the data for all schizophrenia twin studies carried out
prior to 2001 showed a concordance rate for MZ twins of 40% and 7% for DZ twins
, (Family studies) Gottesman (1991) found that as genetic similarity increases, so does the
probability of sharing schizophrenia e.g. children with 2 schizophrenic parents had a
concordance rate of 40% / children with one schizophrenic parent had a concordance rate of 13%
and siblings had a concordance rate of 9%.
(Adoption studies) Tienari et al (2000) (Finland) found that, of the 164 adoptees whose biological
mothers had been diagnosed with schizophrenia, 7% also received a diagnosis of
schizophrenia compared to just 2% of the 197 control adoptees (those born to non-schizophrenic
mothers). (3.5 times greater)
Genetic explanations A03
Point Evidence Conclusion
A weakness of the genetic The genetic explanation This is a weakness of the
explanation for could be seen as overly genetic explanation as it
schizophrenia is that it reductionist as it reduces a may well oversimplify the
could be seen as overly complex mental disorder complex nature of the
reductionist. to a lower level of cause of the disorder
explanation.
Evidence to support the Joseph et al collated the If genetic factors do
genetic explanation for results of studies which determine levels of
schizophrenia comes from have compared the schizophrenia, then the
the meta-analysis of twin concordance rates for more genetically similar
studies conducted by schizophrenia between twins are, the higher the
Joseph. MZ/monozygotic twins concordance rates should
(genetically identical) and be. Therefore, Joseph’s
DZ/dizygotic twins (only study supports the
share 50% of genes). They importance of genetics as
found a concordance rate an explanation for
of 40% for MZ twins but a schizophrenia.
concordance rate of only
7% for DZ twins.
Further support for genetics As Joseph conducted a The population validity of
as an explanation of meta-analysis, the datathe data gathered suggests
schizophrenia comes from gathered and conclusions
that it is possible to
the methodology used by reached apply to a generalise Joseph’s
Joseph. significant sample of MZ
findings and conclusions,
and DZ twins. and this further supports
the genetic explanation.
There is a related problem Twin studies often compare This means that MZ twins
in using twin studies to test concordance rates of MZ may have a higher
the relationship between and DZ twins. However, MZ concordance rate than DZ
genetics and schizophrenia. twins may be treated more twins, but this isn’t
similarly/ have a more necessarily due to their
Revision note: There are similarities between biological explanations for schizophrenia and the
three biological explanations for aggression: genetics, neurotransmitter activity and structural
defects.
Genetics
- Unlike aggression (MAOA-L) and OCD (COMT/SERT) there is no single gene that is linked to
schizophrenia. Instead, there are many candidate gene combinations. Therefore,
schizophrenia is polygenic – Ripke argues there are 108 gene combinations – makes
people more vulnerable
- The genetics explanation for schizophrenia overlaps with the genetic explanation for aggression. The
A01 is similar as the same methodology is used: twin studies, family studies and adoption
studies.
- This therefore means that the A03 also overlaps with the genetic explanations for aggression too as
you can cover the same methodology problems – for e.g. MZ twins may have higher concordance
rates than DZ twins, but this isn’t necessarily due to greater genetic similarity, it could be that MZ
twins are treated more similarly than DZ twins and therefore the higher concordance rate is
produced by a more similar environment
(Discuss this in A01):
Type of method How it works What it should show if schizophrenia
is genetic
Twin study Compare the concordance rates of If schizophrenia is genetic, MZ twins should
the MZ (monozygotic/identical) twins have a higher concordance rate than DZ
who share 100% of their genes with twins
DZ (dizygotic/non-identical) twins
who share 50% of their genes
Family study Identify families who have a family The risk of developing schizophrenia
member with schizophrenia. increases with genetic relatedness / the
Compare the risk of developing closer your relationship to a family member
schizophrenia for their relatives, with schizophrenia, the greater the chance
based on how closely of you developing schizophrenia
related/genetically similar they are
Adoption study Compare adopted children who Adopted children who have a biological
have a biological parent with parent with schizophrenia are more likely
schizophrenia to a control group of to develop schizophrenia than a control
adopted children who don’t have a group of adopted children who don’t have a
biological parent with schizophrenia. biological parent with schizophrenia
(Discuss this in A03):
(Twin studies) Joseph (2004) calculated that the data for all schizophrenia twin studies carried out
prior to 2001 showed a concordance rate for MZ twins of 40% and 7% for DZ twins
, (Family studies) Gottesman (1991) found that as genetic similarity increases, so does the
probability of sharing schizophrenia e.g. children with 2 schizophrenic parents had a
concordance rate of 40% / children with one schizophrenic parent had a concordance rate of 13%
and siblings had a concordance rate of 9%.
(Adoption studies) Tienari et al (2000) (Finland) found that, of the 164 adoptees whose biological
mothers had been diagnosed with schizophrenia, 7% also received a diagnosis of
schizophrenia compared to just 2% of the 197 control adoptees (those born to non-schizophrenic
mothers). (3.5 times greater)
Genetic explanations A03
Point Evidence Conclusion
A weakness of the genetic The genetic explanation This is a weakness of the
explanation for could be seen as overly genetic explanation as it
schizophrenia is that it reductionist as it reduces a may well oversimplify the
could be seen as overly complex mental disorder complex nature of the
reductionist. to a lower level of cause of the disorder
explanation.
Evidence to support the Joseph et al collated the If genetic factors do
genetic explanation for results of studies which determine levels of
schizophrenia comes from have compared the schizophrenia, then the
the meta-analysis of twin concordance rates for more genetically similar
studies conducted by schizophrenia between twins are, the higher the
Joseph. MZ/monozygotic twins concordance rates should
(genetically identical) and be. Therefore, Joseph’s
DZ/dizygotic twins (only study supports the
share 50% of genes). They importance of genetics as
found a concordance rate an explanation for
of 40% for MZ twins but a schizophrenia.
concordance rate of only
7% for DZ twins.
Further support for genetics As Joseph conducted a The population validity of
as an explanation of meta-analysis, the datathe data gathered suggests
schizophrenia comes from gathered and conclusions
that it is possible to
the methodology used by reached apply to a generalise Joseph’s
Joseph. significant sample of MZ
findings and conclusions,
and DZ twins. and this further supports
the genetic explanation.
There is a related problem Twin studies often compare This means that MZ twins
in using twin studies to test concordance rates of MZ may have a higher
the relationship between and DZ twins. However, MZ concordance rate than DZ
genetics and schizophrenia. twins may be treated more twins, but this isn’t
similarly/ have a more necessarily due to their
