18331459
Description
Mind Map by Katie Greensted, updated more than 1 year ago
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Created by Katie Greensted
almost 5 years ago
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Evaluation: Genetic Explanation of
Schizophrenia
- Jessica Wright indicated that
as many as 700 genes have
been linked to schizophrenia
(2014), so by now this figure is
likely to be in the 1000s.
- Schizophrenia can appear in the absence of a
family history of the disorder, which could
suggest that this is due to a mutation in our
genes. These changes to genes can result from an
environmental factor or an error in cell division.
For example, 25% of people with Di George
syndrome develop schizophrenia, and this is a
condition which is caused by the deletion of
genes in chromosome 22.
- The COMT gene has been linked to
schizophrenia, as the link between Sz
and the Di George syndrome may be
due to a deletion of the COMT gene.
These genes provide the instructions
for the creation of an enzyme which
breaks down neurotransmitters such
as dopamine.
- The DISC 1 gene - people with an
abnormality to this gene are 1.4x
more likely to develop Sz (Kim et al).
This gene codes for GABA, which is
a neurotransmitter that regulates
others such as dopamine and
glutamate.
- There are similar trends found in a lot of
different studies from more than one country,
which all support one another's findings. This
suggests that the idea that genes play a part
in the development of schizophrenia is a
reliable explanation.
- The idea that genes are the primary cause of
schizophrenia is extremely reductionist,
particularly since concordance rates are less
than 100% for Mz twins, suggesting that there is
room for environmental influences to 'cause'
schizophrenia.
- The diathesis stress model suggests that behaviour, such as
schizophrenic behaviours, comes from in part a genetic
predisposition which is the triggered by environmental factors.
This could explain why there is not a 100% concordance rate for
Mz twins as one may not experience the same environmental
trigger and therefore not develop the disorder.
- The diathesis stress model suggests that behaviour, such as
schizophrenic behaviours, comes from in part a genetic
predisposition which is the triggered by environmental factors.
This could explain why there is not a 100% concordance rate for
Mz twins as one may not experience the same environmental
trigger and therefore not develop the disorder.
- There is no clear chromosomal abnormality
that is linked to schizophrenia. Although
researchers have found many genes which can
be linked to symptoms of schizophrenia or
predispose someone to Sz, there is no clear
link.
- Schizophrenia can appear in the absence of a
family history of the disorder, which could
suggest that this is due to a mutation in our
genes. These changes to genes can result from an
environmental factor or an error in cell division.
For example, 25% of people with Di George
syndrome develop schizophrenia, and this is a
condition which is caused by the deletion of
genes in chromosome 22.
- Family Studies
- Schizophrenia has been found to have a strong
heritable factor. Gottesman's family study into
schizophrenia (1991) found that the concordance rate
for schizophrenia in the general population was
1%, whereas it was 48% for Mz (identical) twins.
This suggests that the greater the degree of
genetic relatedness, the higher the risk of
developing schizophrenia is.
- However, the fact that Gottesman's results
suggested the concordance rate for Mz twins
was only 48% suggests that there must be
other factors influencing the development of
schizophrenia, otherwise the concordance rate
would be 100% in identical twins.
- Concordance rates in families may be more
to do with common rearing patterns or
other environmental factors (particularly in
Mz twins because they look identical so are
treated identically a lot of the time).
- Concordance rates in families may be more
to do with common rearing patterns or
other environmental factors (particularly in
Mz twins because they look identical so are
treated identically a lot of the time).
- However, the fact that Gottesman's results
suggested the concordance rate for Mz twins
was only 48% suggests that there must be
other factors influencing the development of
schizophrenia, otherwise the concordance rate
would be 100% in identical twins.
- Schizophrenia has been found to have a strong
heritable factor. Gottesman's family study into
schizophrenia (1991) found that the concordance rate
for schizophrenia in the general population was
1%, whereas it was 48% for Mz (identical) twins.
This suggests that the greater the degree of
genetic relatedness, the higher the risk of
developing schizophrenia is.
- Twin Studies
- Researchers use twin studies to investigate the
influence of nature and nurture as Mz twins
share 100% of their genes whereas Dz twins only
share 50%. Gottesman and Shields (1966) found
that the concordance rate of Mz twins was 42%
compared to Dz twins which was only 9%.
Similarly to Gottesman's later family study, this
suggests genes do have an influence, however as
the figure for Mz twins is not 100%, it is not
based on genetics alone.
- Twin studies often have very small
sample sizes and therefore the results
have low population validity. This means
it is difficult to generalise them to the
general population.
- Twin studies often have very small
sample sizes and therefore the results
have low population validity. This means
it is difficult to generalise them to the
general population.
- Researchers use twin studies to investigate the
influence of nature and nurture as Mz twins
share 100% of their genes whereas Dz twins only
share 50%. Gottesman and Shields (1966) found
that the concordance rate of Mz twins was 42%
compared to Dz twins which was only 9%.
Similarly to Gottesman's later family study, this
suggests genes do have an influence, however as
the figure for Mz twins is not 100%, it is not
based on genetics alone.
- Adoption studies
- Adoption studies are used
by researchers as it allows
them to disentangle
genetic and environmental
influences.
- Heston found that the concordance rate in the
control group of adoptees (no history of Sz in
biological family) was 0%, whereas in the group
where the adoptee's biological mother had
schizophrenia, the concordance rate was 16%.
This suggests there is a biological influence in
the development of Sz. This is backed up by
Tienara who found similar figures (control = 1%,
bio mother with sz = 10%)
- Fewer than one third of people with Sz
have a family history of the disorder, which
suggests that there is a complexity in the
genes in question and may not be as simple
as just inheriting a gene from your parents.
- Fewer than one third of people with Sz
have a family history of the disorder, which
suggests that there is a complexity in the
genes in question and may not be as simple
as just inheriting a gene from your parents.
- Heston found that the concordance rate in the
control group of adoptees (no history of Sz in
biological family) was 0%, whereas in the group
where the adoptee's biological mother had
schizophrenia, the concordance rate was 16%.
This suggests there is a biological influence in
the development of Sz. This is backed up by
Tienara who found similar figures (control = 1%,
bio mother with sz = 10%)
- Adoption studies are used
by researchers as it allows
them to disentangle
genetic and environmental
influences.
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