1. Causes of schizophrenia

2. 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

3. Starter
In pairs, discuss how the biological approach may explain schizophrenia i.e. what causes schizophrenia?
Genetic explanations
Biochemical explanations
Brain structure
Season of birth

4. 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

5. 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

6. Q) What does this suggest about schizophrenia?
A graph to show the genetic risk of developing schizophrenia.
Source: Zimbardo et al (1995)
Q) What does this suggest about schizophrenia?

7. 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 cross-section of people already diagnosed
Can’t differentiate between genetic and environmental influences
Prospective (longitudinal studies) used to provide more reliable data…

8. 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 years at start of study
Matched on age, gender, parental socio-economic status and urban/rural residence

9. 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 )

10. 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)

11. 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

12. 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…

13. 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

14. 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

16. 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)

17. 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

18. 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

19. 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