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

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

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.

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 ?

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

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?

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.

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?

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?

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

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.

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?

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?

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

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