Transcript Causes of schizophrenia

Causes of schizophrenia
Learning Objectives
By the end of this lesson you will:
Be able to discuss how the biological
approach explains schizophrenia
Have developed your research skills
Be able to make a mind-map on the
biological causes of schizophrenia
Starter
In pairs, discuss how the biological
approach may explain schizophrenia
i.e. what causes schizophrenia?
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Genetic explanations
Biochemical explanations
Brain structure
Season of birth
Genetic explanations
Schizophrenia runs in families
Could be because families share
same disadvantaged background?
Research suggests genetic factors
are important:
• Family studies
• Twin studies
• Adoption studies
Family Studies
1st degree relatives (parents, siblings
and offspring) share an average of
50% of their genes
2nd degree relatives (half siblings,
grandparents/children, aunts/uncles)
share approx 25% of their genes
To investigate genetic transmission of
schizophrenia, studies compare rates
of schizophrenia in relatives of
diagnosed cases compared to
controls
A graph to show the
genetic risk of developing
schizophrenia.
Source: Zimbardo et al
(1995)
Q) What does this suggest about
schizophrenia?
Kendler et al (1985) found that 1st
degree relatives of those with
schizophrenia are 18 times more at
risk than the general population
Problems with family studies?
• Often inconclusive as conducted
retrospectively – compare a crosssection of people already diagnosed
• Can’t differentiate between genetic
and environmental influences
• Prospective (longitudinal studies)
used to provide more reliable data…
The Copenhagen High-Risk Study
(Kety et al. 1962)
Kety and collegues identified 207
offspring of mothers diagnosed with
schizophrenia (high risk) along with a
matched control of 104 children with
‘healthy’ mothers (low risk) in 1962
Children aged between 10-18 years
at start of study
Matched on age, gender, parental
socio-economic status and
urban/rural residence
Follow-up studies conducted in 1974 and
1989
Results:
• Schizophrenia diagnosed in 16.2% of high
risk group compared to 1.9% in low risk
group
• Schizotypal personality disorder diagnosed
in 18.8% of high risk group vs 5% of low
risk group
(Schizotypal Personality = A disorder characterized by eccentric
behaviour and anomalies of thinking and affect which resemble
those seen in schizophrenia, thought no definite and characteristic
schizophrenic anomalies have occurred at any stage )
Combining the figures for the 2
disorders = 35% in high-risk group
and 6.9% in low-risk group
Similar findings found in the New York
High Risk Project = 25 yr follow-up
(Erlennmeyer-Kimling et al. 1997)
Twin Studies
Compare concordance rates for identical
(MZ) and fraternal (DZ) twins
Both share the same environment but only
MZ twins have identical genetics
Many studies conducted – all show much
higher concordance rate in MZ than DZ
twins
To separate environment from genetic
influences, researchers have sought out
MZ twins reared apart where at least 1 has
been diagnosed with schizophrenia
Gottesman & Shields (1982)
Used the Maudsley twin register and
found 58% (7/12 MZ twins reared
apart) were concordant for
schizophrenia
If the genetic hypothesis is correct, then
the offspring of a non-affected
discordant MZ twin should still be
high-risk…
Fischer (1971)
Found that 9.4% of such offspring
developed schizophrenia, which is a
much higher incidence than in the
general population (1%)
A study in London using the Maudsley
Twin Register (Cardno et al. 1999)
found a 40% concordance rate in MZ
twins, compared to 5.3% in DZ twins
AO2 of twin studies
Discuss in pairs some evaluative points on
twin study research
• Twins often reared in same environment so
cant separate genetic and environmental
factors
• The number of MZ twins reared apart are
few in number
• Reason MZ twins reared apart may be due
to problems in the family
• Even twins reared apart shared the same
environment in the womb before birth =
environmental factors cant be discounted
Adoption Studies
More effective in separating effects of
genetic and environmental factors
Look at adopted children who later develop
schizophrenia and compare to biological
parents
The Finish Adoption Study (Tienari, 1969)
Identified adopted offspring of biological
mothers with schizophrenia (112 cases)
Matched control group (135 adopted
offspring of non-schizophrenic biological
mothers)
Adoptees ranged from 5-7 yrs at the start
of the study – all had been separated from
mothers before 4
Study checked children again in 1987
Reported 7% of high risk group developed
schizophrenia compared to 1.5% of
controls.
The Danish Adoption Study (Kety et al. 1994)
Took a national sample across Denmark
Found high rates of diagnosis for chronic
schizophrenia in adoptees whose biological
parents had the same diagnosis, despite
living with ‘healthy’ parents
AO2 of Adoption studies
Data provided by prospective studies
suggest a strong genetic link for
schizophrenia
Longitudinal studies are hampered as
diagnostic criteria for schizophrenia is
constantly being updated and
changed
AO2 of genetic explanations
Twin, adoption and family studies
continues to provide reliable evidence that
the degree of risk increases with degree of
genetic relatedness
No twin study has yet shown 100%
concordance in MZ twins
Studies conducted so far don’t tell us which
genes might be important for the
transmission of schizophrenia.
= genetic risk
?
symptoms