Causes of schizophrenia The Genetic Explanation

Learning Objectives By the end of this lesson you will: Be able to outline how the genetic approach explains schizophrenia Have many evaluative points at your disposal for the exam Have revisited key aspects of the research methods (AO3) content

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

Genetic explanations Schizophrenia runs in families But we can’t assume it’s inherited; eg. could be that families share same disadvantaged background..? Environmental Factors! Research suggests genetic factors are important: Family studies Twin studies Adoption studies

These concordance rates suggest that schizophrenia is caused by our genes. A graph to show the genetic risk of developing schizophrenia. Source: Zimbardo et al (1995)

Although Kendler et al (1985) found that 1 st degree relatives of those with schizophrenia are 18 times more at risk than the general population, family studies: Are often inconclusive as they’re conducted retrospectively – compare a cross-section of people already diagnosed Therefore can’t easily differentiate between genetic and environmental influences But prospective (longitudinal studies) can be used to provide more reliable data… Problems with family studies

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

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 ) The Copenhagen High-Risk Study (Kety et al. 1962)

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) The Copenhagen High-Risk Study (Kety et al. 1962)

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 12 MZ twins who had been raised apart where at least one of the pair had schizophrenia In 58% of cases (7 out of the 12 MZ twin pairs reared apart) it was found that the other twin also developed schizophrenia AO2: so even when there is no shared upbringing / environment, we still see high concordance for MZ twins. Points to factors related to NATURE not NURTURE.

AO2 of twin studies Twins often reared in same environment so cant separate genetic and environmental factors The number of MZ twins reared apart are few in number – therefore cannot easily generalise on such a small sample Reason MZ twins reared apart may be due to problems in the family which could have been a starting point for psychosis 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 Finnish 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 Finnish Adoption Study (Tienari, 1969)

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