4. Genetics – Twin Studies
• Gottesman 1991 suggests that
schizophrenia is inherited through
genes. Studied 40 twins - the
concordance rate for MZ twins is
about 48% and only about 17% for
DZ twins.
• Also Cardno 2002 – showed
concordance rate of 26.5 MZ and
0% for DZ.
5. Evaluation – Twin Studies
• However, the fact that the concordance rate for twins is
not 100% means that Schizophrenia cannot be accounted
for by genetics alone
• As we already know, the higher concordance between
MZ twins could be explained by greater environmental
similarity rather than genetic similarity – MZ twins elicit
more similar treatment than DZ twins (so can be
explained by other theories)
• Also the sample size of such twin studies is always going
to be very small, so ……..
6. Further Twin Evaluation
Twin studies do not all use the same diagnostic
criteria – Therefore different diagnosis will
produce different concordance rate.
Concordance rates can also be calculated
differently depending on the method used –
questions the reliability of such studies.
7. Genetics - Adoption Studies
• Tienari – 155 adopted children –
who biological mothers had
schizophrenia –they had a
concordance of 10% compared to 1%
in adopted children without
schizophrenic parents.
• This is very strong evidence that
genetics are a risk factor for
schizophrenia
8. Genetics – Family Studies
• Gottesman also studied families – he
concluded that if both your parents
suffer from Schizophrenia, then you
have a 46% chance of developing it
yourself (compared to a 1% chance of
someone selected at random will
suffer)
• The more genetically similar relatives
are, the more concordance is found.
9. Family Evaluation
• This evidence again strongly suggests
genetics is a factor
However:
• It could also be explained in terms of the
fact that genetically similar family
members tend to spend more time
together and so environment could also
affect.
10. Biochemical Factors – The
Dopamine Hypothesis
• This theory claims that excessive
amounts of dopamine or an
oversensitivity of the brain to
dopamine is the cause of schizophrenia
• Eval: There is strong empirical support
which suggests that dopamine plays an
important role in schizophrenia – e.g
drugs which block dopamine
(Phenothaiazines) also seem to reduce
the symptoms of schizophrenia.
11. The Dopamine Hypothesis -
Evaluation
• L-Dopa – a drug for Parkinson’s disease
actually increases dopamine – this in turn
can produce symptoms of schizophrenia.
• Post mortems of schizophrenics, show an
increase of dopamine in parts of the brain.
(Seeman 1987)
12. Dopamine Evaluation - Negatives
• Phenothiazines do not seem to work for everyone
therefore....
• Cause or effect?
• This theory is over simplistic and has been
criticized for using the treatment to determine
the cause. This is an AETIOLOGY FALLACY
13. Neuroanatomy - Brain Structure
There is growing evidence that
schizophrenia is down to physical
abnormalities in the brain.
Szesko et al found that the ‘asymmetry’
found in normal brains – in the prefrontal
cortex is absent in people with
schizophrenia.
14. Brain Structure
People with
schizophrenia have
abnormally large
ventricles in the brain.
Ventricles are fluid
filled cavities. This
means that the brains
of schizophrenics are
lighter than normal.
15.
16. Brain Structure Evidence
• Andreasen et 1990 – conducted a
very well controlled CAT scan
study and found significant
enlargement of the ventricles in
schizophrenics compared to
controls.
• However this was only the case
for men and not for women.
Therefore cant generalise to
everyone.
17. Evaluation
• Research is difficult to interpret and there
have been contradictory findings.
• Difficult to establish cause and effect – as
many participants have suffered from
schizophrenia for a while and have been
undergoing treatment. So.......
18. Further Evaluation
• The main problem with such
studies is that it is not found in
all schizophrenics. This has lead
to further research done by
Crow 1985.
• He suggested two types of
schizophrenia with two
biological causes.
19. Two Syndrome Hypothesis - Crow 1985
• Type one - genetically inherited
associated with dopamine –
characterised by positive
symptoms.
• Type Two – Neurodevelopmenal
disorder – to do with Brain
structure – characterised by
negative symptoms.
20. Summery
• Biological explanations do
account for schizophrenia,
however the fact that there is no
conclusive explanation that
accounts for all schizophrenics –
psychological explanations need
to be considered.
21. Exam Question
• TASK: Exam Question: PLAN THE QUESTION
• Outline and evaluate one or more biological
explanations for schizophrenia. In your
evaluation you should refer to research
evidence. (25 marks)
