Explanation and Evaluation of the Genetic Theory of Schizophrenia

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  • Created by: Lisgoe
  • Created on: 04-11-14 17:15
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  • Genetic Theory
    • Gottesman
      • Higher concordance rate of individual developing Sz if they have a close family member with the disorder
        • 1% risk for general population
        • 46% with 2 parents who suffer from Sz
      • Likilhood of individual developing Sz is proportional to DNA shared
        • MZ twins = 48%
        • DZ twins = 17%
        • Grandchildren = 5%
        • 46% with 2 parents who suffer from Sz
        • 1% risk for general population
    • Monozygotic Twins (MZ)
      • 1 egg fertilized
        • Share 100% DNA
    • Dizygotic Twins (DZ) (Fraternal twins)
      • 2 eggs fertilized
        • Share 50% DNA
    • Disorders tend to be genetically passed on
      • Suggests a genetic basis for Psychopathology
    • Evidence For
      • Cardno et al (2002)
        • Based on Maudsley Twin Register
          • Used strict diagnostic criteria
          • Showed a concordance rate of 26.5 for MZ twins and 0 for DZ twins
            • Suggests that similarities in DNA show the likelihood of Sz is higher, compared to DZ twins that share less DNA
      • Advances in research
        • Now easier to assess zigoticity accurately
          • Implications of this enables doctors to accurately calculate the concordance rate of a child developing Sz if their twin has Sz
      • Adoption Studies
        • Tienari (1991)
          • "Finnish Adoption Study"
            • Found 115 adopted children
              • Biological parents sufferers of Sz
              • Compared them to a matched group of adopted children
                • No family with Sz
                • Found 10% development in G1
                  • Suggests Sz is more biological than psychological
                    • Due to strong genetic evidence
                    • 1% in G2
                • 1% in G2
        • Provides evidence for genetic component of development
        • Methodological flaws with some adopted studies
          • Affects validity
          • Doesn't take into account environmental factors
    • Evidence against
      • Rarity of MZ twins
        • Only 1% would be expected to develop Sz
          • Sample sizes are small
            • Unable to generalise to general population
      • Different diagnostic criteria
        • Between MZ and DZ twins
          • Comparisons can't be made
            • Different concordance rates are calculated
      • Concordance calculated differently
        • Using different methods
          • No consistency
      • "Blind" interviewers
        • Found lower concordance rates
          • Higher the control, the lower the rate (Marshall (1990)

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