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? 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

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?

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…

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