1. Schizophrenia Specification details: Pages 201-204 of Year 2 book
Biological explanations for schizophrenia: genetics, the dopamine hypothesis and neural correlates.

2. Biological explanations of Schizophrenia
Genetic factors
Neurochemicals: Dopamine hypothesis
Brain structure

3. Assumptions of biological explanations
All mental disorders have a physical cause. (micro-organisms, genetics, biochemistry or neuroanatomy)
Mental illnesses can be described in terms of clusters of symptoms.
Symptoms can be identified, leading to the diagnosis of an illness.
Diagnosis leads to appropriate physical treatments.

4. Schizophrenia: genetics factors
Prevalence of schizophrenia is the same all over the world (about 1%)
Supports a biological view as prevalence does not vary with environment
However, there are variations within broad geographical areas (e.g. Torrey 2002 – found high rates of Sz in Ireland, 4% of the population, the incidence is also high in Croatia and Scandinavian countries but low in Spain and Italy and very low in some parts of Africa)
A problem of reliability of diagnosis or influence of environmental factors ?

5. How do we study the influence of genetic factors?
Concordance rate: the proportion of pairs where both individuals share a certain characteristic.
If the concordance rate is 100% in MZ twins it means that the characteristic is genetically determined.
If it less than the 100% but higher that DZ twins What does it mean?
Twin studies
However they might be treated differently
However one is usually born bigger than the other
Dizygotic twins
Monozygotic twins
Share as many genes as siblings but share the same environment
Share the same genes and the same environment

6. Family studies
Adoption studies
If the adopted children have a higher concordance rate for Sz with their biological parents than with their adoptive parents, does it support the influence of genetic factors?
Children share 50% of their genes with each of their parents. If one of their parent is schizophrenic has the child more chance to be schizophrenic? If he/she is Sz, are only genetic factors responsible?

7. Twin studies
Gottesman and Shields ( reviewed the results of 5 twin studies looking for concordance rates for schizophrenia. These studies looked at 210 MZ twins and 319 DZ twins
It was found that in MZ twins there was a concordance rate of 35-58% compared with dizygotic (DZ) twin rates that ranged from 9-26%. They also found a concordance rate in MZ twins of 75-91% when the sample was restricted to the most severe form of schizophrenia.

8. Are these diagnosis made using the same criteria?
The milder forms of schizophrenia had concordance rates of 17-33% suggesting that there may be greater genetic loading with severe forms of schizophrenia. The twin studies have all assumed that the shared environmental effects for MZ and DZ twins are equal which may be incorrect
Twins are not representative of the wider population. (gestational environment)
It is a very small sample. There are very few MZ twins in the population and only 1% are Sz.
Are these diagnosis made using the same criteria?

9. Adoption studies
Prevalence amongst biological relatives
Prevalence among adoptive relatives
Kety et al (1968) schizophrenia only
13% 2%
Tienari et al (1994) all ‘severe’ psych. diagnoses
30%
15%
Could the psychiatrist making the diagnosis in the child be influenced if he/she is aware that one of both of the parents are Sz??
Were they adopted by members of the extended family?
Were these diagnosis made using the same criteria?
Did they see their biological parents regularly?
How old were children when they were adopted?

10. The overall picture
This seems to indicate an influence of genetic factors but also the importance of environmental/ social factors

11. So have we found a gene responsible for Sz?
In 2006, an Edinburgh University team found people carrying a variant of a gene called neuregulin had a higher chance of developing psychotic symptoms. However since then research has shown that Sz involves a huge number of genes with each of them making only a small contribution to the development of the disorder according to Robin Murray a leading schizophrenia researcher.

12. Risk rises with degree of genetic relatedness
Spouse – 1% (same as general population)
Child – 13%
DZ twin – 17%
MZ twin – 48%
Effect of shared environment?

13. Substantial evidence for a genetic contribution
Some evidence disputed:
Shared environment issues
Diagnostic criteria in adoption studies
All the evidence also suggests environmental triggers: Epigenetics could explain that the concordance rate is less than 100% in MZ twinsHeritability is similar with other major disorders such as breast cancer, hypertension, etc
How is schizophrenia inherited and what exactly is inherited?

14. Gender bias Reductionism Ethnocentrism Nature/Nurture Approach
is the theory based on research carried out on an unrepresentative sample?
Gender bias
does the theory/approach attempts to explain phenomena in terms of basic elements?
Reductionism
is the theory based on research carried out in one particular type of culture (i.e. indivicualistis culture) ?
Ethnocentrism
Does the theory/approach explain phenomena in terms of nature i.e. gentics neglecting other factors i.e. social factors?
Nature/Nurture
Situate the theory in one approach (biological, behavioural, cognitive, psychodynamic)
Approach
Does the theory/approach acknoledge a sense of individual free-will or does it argue that our behaviour is determined by a particular set of factors?
Determinism
Does the theory/approach propose/research issues which could be socially controversial ? (i.e. correlation between race and IQ)
Ethics
Is the theory based on evidence which is objective/ valid/ reliable?
Scientific method

15. Exam Question
Prepare for this timed question for next lesson Discuss biological explanations for schizophrenia. (16 marks)