Download Schizophrenia - Psychology: Teaching and Learning

The Biological Explanations
of
Schizophrenia
1. Genetics
2. Biochemistry
3. Evolutionary Theory
3 x Biological Explanations
1. Genetics – Twin & family studies
2. Biochemistry - Dopamine Hypothesis
3. Evolutionary Theory - Group Splitting Hypothesis
They say…
“.. A picture paints a thousand words ..”
ACTIVITY –
Pictures only -presentations
1. GENETICS – Twin + adoption studies + Eval.
2. BIOCHEMISTRY – Dopamine Hypothesis + Eval.
3. EVOLUTIONARY THEORY – Group Splitting
Hypothesis + Eval.
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FOR INFO
1. Genetic causes of
schizophrenia
Genes
Not those ..
Genetic causes of schizophrenia


Being genetically related to someone with
schizophrenia can significantly increase a person’s
chances of developing it.
Family and twin studies have looked at concordance
rates.
TWIN RESEARCH

Concordance rates are
the chances that
someone will develop
a disorder if they
related to someone
who has it.
TWIN RESEARCH

For example Gottesman (1991) reviewed about 40
studies and found that with identical (MZ) twins
there was a 48% chance of both being
schizophrenic. With non-identical (DZ) twins there
was a 17% chance of developing schizophrenia.
Evidence for...

Shields (1962) found that MZ twins who were raised
in different in families still showed around a 50%
concordance rate for the development of
schizophrenia.
Evidence for...

Adoption studies have found that when children are
adopted because one or both of their biological
parents has schizophrenia, the chance of them
developing it is still the same. This suggests that
genetics are more significant than the environment.
Evidence against....

No study has found 100% concordance rate, so
schizophrenia cannot just be caused by genes.
Shared environment may be cause higher
concordance rates in family studies because
children imitate ‘schizophrenic’ behaviours from
relatives.
Evidence against....

This means other factors need to be considered e.g.
biochemical or psychological factors.
The genetic causes of schizophrenia

Genes-attempts to identify specific genes
responsible for this illness have not been successful.
Claims were made about genetic markers on
chromosomes 5 & 22 but these have been
retracted.
The genetic causes of schizophrenia


Schizophrenia has a tendency to run in families. A
child of a schizophrenic mother has a 6% chance
of developing schizophrenia, compared to a 1%
chance if unrelated.
How can we investigate genetics?
Family studies:

Children with two
schizophrenic
biological parents are
46% more likely to
develop the disorder.
These studies do not
rule out environmental
learning though.
The Copenhagen high risk study (Kety et al, 1962)


The Copenhagen high risk study (Kety et al, 1962)
identified 207 children whose mothers had
schizophrenia (high risk) along with 104 children
with healthy mothers (low risk).
They were aged between 10 and 18 years at the
start of the study and were matched on age,
gender, parent socio-economic status and
urban/rural residence.
The genetic causes of schizophrenia

A follow up of these children was conducted in
1974 and 1989, and the results were published in
1993 by Parnas et al. These results strongly
suggested a genetic link, as schizophrenia was
diagnosed in 16.2% of the ‘high-risk’ group, and
only 1.9% of the ‘low-risk’ group. Schizotypal
personality disorder was diagnosed in 18.8 % of
the ‘high-risk’ group, and in 5% of the ‘low-risk’
group.
What does this research tell us about schizophrenia?
Cross-cultural research - Twin studies:

...studies from many countries have produced
different estimates. (narrow/broad) but Gottesman
(1991) suggests that monozygotic (identical twins)
who have the same genes have slightly higher
concordance rates (48%) for schizophrenia than
dizygotic (non-identical) twins (17%) Concordance
rates refer to whether both twins develop this
disorder. However identical twins also share the
same environment.
The genetic causes of schizophrenia

Gottesman and Shields (1972) investigated 45,000
individuals treated at a London hospital and
identified 57 sets of twins who agreed to take part
in the study. They identified a 42% concordance
rate for MZ twins and only 9% for DZ twins.
What does this tell us about schizophrenia?

Klaning et al (1996)
cite that it may be due
to twins' greater
exposure to perinatal
complications that they
develop later
disorders.
Adoption studies...

where the adopted subjects environment are
matched, the rates of schizophrenia are higher for
adoptive children with schizophrenic biological
parents compared to adoptive children with nonschizophrenic parents (Kety et al1975) ideally
identical twins with schizophrenia raised in different
adoptive environments would be the best evidence
for genetic causes but obviously these cases are
extremely rare.
The genetic causes of schizophrenia

Tienari (1991) examined the rate of schizophrenia
in Finnish people who had been adopted and
whose biological mothers were schizophrenic. As
predicted a biological mother with schizophrenia
increased the rate of schizophrenic in the adoptees,
even if they were adopted by non-schizophrenic
families.
Tienari (1991) continued

But the schizophrenic genetics revealed itself only if
the adopted family was psychologically disturbed
in some way. So, vulnerable individual could be
protected from schizophrenia if their family of
rearing were healthy.
Family studies continued:

Heston (1966) compared 47 children of
schizophrenic mothers adopted before the age of
one month, with 47 children raised in the home of
their biological and non-schizophrenic mothers.
Family studies continued:

Heston found that many of the children with
schizophrenic mothers developed schizophrenia,
whereas none of the children from nonschizophrenic mothers developed schizophrenia. This
is the same as in the normal population.
Evaluation

It seems that heritability is an important component
to any medical condition such as CHD, hypertension
or diabetes (Lilienfeld 1995). The precise mode of
inheritance remains controversial.
Evaluation continued


The most popular view is the multifactorial
(polygenic) model: a number of genes are involved
that determine a predisposition which requires
environmental factors such as stress to trigger the
symptoms.
According to Claridge and Davis (2003), the
contribution of genetic influences is one of the few
certainties about schizophrenia