AO1 theory: The fact that schizophrenia tends to run in families led to the inference that it has a genetic basis. According to the genetic hypothesis, the more closely related the family member to the schizophrenic the greater their chance of developing the disorder. Concordance rates, which show the percentage of family members developing schizophrenia, are investigated as research evidence. The comparison is the 1% probability of schizophrenia in the general population.
Evidence from family studies:
- First-degree relatives (offspring, parents and siblings) share 50% of their genes, second-degree relatives share 25%.
- Family studies involve the comparison of rates of schizophrenia in relatives of diagnosed cases compared with relatives of controls.
- There is evidence that the closer the biological relationship, the greater the risk of schizophrenia developing.
-> Kendler et al. (1985): first-degree relatives of those with schizophrenia are 18 times more at risk compared to the general population.
Key study: Kety et al. (1994)
- High-risk group: 207 offspring of schizophrenic mothers.
- Low-risk group: 104 control children with healthy mothers.
- Children aged 10 to 18 and were matched on age/gender/socio-economic status. Follow up testing on children was conducted.
- Schizophrenia was diagnosed in 16.2% of highrisk group. Only in 1.9% of low-risk group.
- prospective study which follows the development of schizophrenia -> more reliable data & does not rely on retrospective data (not always reliable)
- matching of relevant variables in children e.g. socio-economic status
- Can’t differentiate between genetic and environmental influences as there is a shared environment between children and mother
- Many studies e.g. Kety et al., began before the more effective diagnostic systems were developed so it is possible that there was variation in symptoms for original diagnosis of schizophrenia.
Evidence from twin studies
- Twin studies compare the difference in concordance rates (the likelihood of both twins being affected with the disorder) between identical (Monozygotic- MZ) and non-identical (Dizygotic- DZ) twins.
- Only the MZ twins have identical genes.
- A higher concordance rate in MZ compared to DZ twins would suggest a genetic contribution
- MZ twins reared apart can be used to distinguish the effects of genetics and environment.
Gottesman and Shields (1982): 58% of twins who were reared apart, were concordant for schizophrenia. Even MZ twins that…