OCR Psychology A Level Book 2 sample

The Genain quadruplets The Genains were identical (monozygotic) female quadruplets born in 1930. They were given the name ‘Genain’ to protect their real identities — it means ‘dreadful gene’. All four girls developed schizophrenia before the age of 24 years (Mirsky et al. 2000). The Genain case is strong evidence for the genetic explanation because the girls had identical genes. There were also histories of mental illness in both their mother’s and father’s families. But there is also evidence of environmental influences. The father physically abused the girls and was ‘irritable, abusive and intrusive’ (Mirsky et al. ). Both parents were very harsh and sometimes harsher to one girl than another. As adults, the severity and precise nature of their disorders differed greatly. This suggests that their life experiences also played a role in the development of their schizophrenia. Heritability The extent to which a behaviour has a genetic basis can be expressed in terms of ‘heritability’, given as a figure between 0 and 1 (or as a percentage between 0 and 100%). A value of 1 (or 100%) means the variation of the behaviour in a population is entirely due to genetic factors. The heritability of depression is thought to be about 0.37 (37%) (Sullivan et al . 2000). Heritability of schizophrenia is as high as 0.8 (80%) (Stefanis and Stefanis 2010), which makes it one of the most heritable of any common disorder. Heritability varies from one type of specific phobia to another (see below left). Genetic explanation of specific phobias Twin studies Results from twin studies are inconsistent. Ken Kendler et al . (1992) found concordance rates for animal-type specific phobias were 25.9% for MZ twins and 11% for DZs, implying genetic causation. However, they found no significant differences in concordance rates for blood–injection–injury or situation-specific phobias. Ingunn Skre et al . (1993) found no differences between MZ and DZ rates for any type of specific phobia. Association studies No association studies of specific phobias have been carried out to date. But Takeshi Otowa et al. (2016) combined the results of many GWAS of several anxiety disorders, including phobias. They found several genes that may eventually turn out to contribute to the development of anxiety disorders in general (e.g. chromosome 3). But it is not possible on the basis of this study to identify genes involved uniquely in specific phobias. Genetic explanation of schizophrenia Family studies The lifetime risk of developing schizophrenia is about 1% in the general population (baseline risk). But according to Brian Riley and Ken Kendler (2005), the risk is about ten times greater than baseline for the first degree relatives of a person with schizophrenia (e.g. siblings, children). This is strong but not conclusive evidence of a genetic element to the causation of schizophrenia. The key research for this topic, Gottesman et al. ’s study, illustrates the increased risk that children have of developing schizophrenia if their parents have that, or another, disorder. For example, a child with one parent with schizophrenia has a 7% risk of being diagnosed with the same disorder, compared with a 1.12% risk of diagnosis for the general population. Twin studies According to Stephen Glatt (2008), a range of twin studies show that the concordance for schizophrenia in MZ twins is about 46% to 53%. In other words, if one MZ twin develops schizophrenia the other has a 46% to 53% chance of also developing it. On the other hand the concordance in DZ twins is about 15%. The greater concordance for MZs strongly implies a substantial genetic component to schizophrenia. Adoption studies The Finnish Adoptive Family Study by Pekka Tienari et al . (1994) found that the lifetime schizophrenia risk for adopted-away children of biological mothers who had schizophrenia was 9.4%. The corresponding figure for adopted-away children of unaffected biological parents was 1.2%. This difference strongly suggests that genetic influences have an important role in schizophrenia. Association studies The multifactorial polygenic (MFP) model claims that many individual genes each confer a small increased risk of schizophrenia. But in combination, the genetic contribution overall is substantial. This view of schizophrenia causation is supported by both CGAS and GWAS. For example, Stephan Ripke et al . (2014) conducted a GWAS, comparing genotypes of 36,989 people with schizophrenia and 113,075 non-affected control participants. They found that 108 separate genetic variations were associated with increased risk of schizophrenia. The genetic causation of specific phobias is complex. Kendler et al . (1999) calculated 59% heritability for blood– injection–injury phobias and 47% for animal phobias. The results from another study also by Kendler (see text above) found quite different figures for animal-type specific phobias. Identical (MZ) quadruplets are very very rare, and the Genain quadruplets (below) were even more rare. check your understanding 1. Explain what is meant by the term ‘concordance rate’. 2. Outline one study into the genetic explanation of schizophrenia. 3. Of the three disorders on this spread, which would you say is the most heritable, the least heritable and which is in-between? Briefly describe three pieces of evidence to justify your answer. 4. Outline the role of the serotonin transporter gene in depression. 5. Briefly outline what research tells us about the heritability of specific phobias. 6. Outline one similarity and one difference between the genetic and biochemical explanations of mental illness. 25 Background: The genetic explanation of mental illness