Gottesman and Shields: Twin Study of Schizophrenia
Aim:
To investigate to what extent schizophrenia is genetic. To investigate the relative importance of genetic and environmental influences on schizophrenia by comparing MZ and DZ twins.
Procedure:
Records of twins from the Maudsley and Bethtem Royal Joint Hospital provided a sample of 57 twin pairs – 24 MZ, 33 DZ, age range 19 – 64.
Twins were tested for zygosity using blood tests and finger prints as well as visual appearance.
In addition to the hospital diagnosis, the following information was obtained:
Grade 1: both client and co-twin have been hospitalised and diagnoses with schizophrenia.
Grade 2: both client and co-twin have had psychiatric hospitalisation but the co-twin has a different diagnosis.
Grade 3: The co-twin has some psychiatric abnormality (e.g. out-patient care, GP care, neurotic or psychotic personality profile or being abnormal on interview)
Findings:
Grade 1 – MZ = 42%, DZ = 9%
(Grade 2 – MZ = 12%, DZ = 9%; Grade 3 – MZ =25%, DZ = 27%)
Conclusion:
Genes appear to play an important role in schizophrenia because the concordance rate is higher in MZ twins than DZ twins. However environmental factors must also be important as the concordance is not 100%.
Evaluation:
Generalisability:
A large sample was used including different ages and both male and female patients meaning the findings could be generalised. However as the sample only focused on twins this means the findings may only be generalised to twins. Also only one hospital was used.
Reliability:
Sampling was carefully controlled using multiple measures to make sure that twins were correctly allocated either MZ or DZ twin status, and a lot of data was gathered using multiple research methods to check the diagnoses were correct. However interviews and self report data may be less reliable.
Application:
If there is a genetic component for Schizophrenia this is useful because it can help lead to identifying specific genes.
Other evaluation points:
Other studies support findings of MZs sharing traits – Bailey (2000) concordance rates for homosexuality – MZs 24% females, 20% males these figures were much lower for DZ twins
If schizophrenia was entirely a product of genes the concordance rates for MZs would be 100% - this is not the case so environmental factors must play a role
Twins may be treated the same or may copy each other, therefore higher concordance due to environmental rather than biological factors
The study did not look at reasons for schizophrenia or forms of schizophrenia therefore it is limited in its use – it simply identifies a concordance between schizophrenia and genes
Aim:
To investigate to what extent schizophrenia is genetic. To investigate the relative importance of genetic and environmental influences on schizophrenia by comparing MZ and DZ twins.
Procedure:
Records of twins from the Maudsley and Bethtem Royal Joint Hospital provided a sample of 57 twin pairs – 24 MZ, 33 DZ, age range 19 – 64.
Twins were tested for zygosity using blood tests and finger prints as well as visual appearance.
In addition to the hospital diagnosis, the following information was obtained:
- case histories based on a self-report questionnaire and interview with the twins and their parents to provide a record of verbal behaviour
- a personality test
- a test used to measure disordered thinking conducted on twins and parents
Grade 1: both client and co-twin have been hospitalised and diagnoses with schizophrenia.
Grade 2: both client and co-twin have had psychiatric hospitalisation but the co-twin has a different diagnosis.
Grade 3: The co-twin has some psychiatric abnormality (e.g. out-patient care, GP care, neurotic or psychotic personality profile or being abnormal on interview)
Findings:
Grade 1 – MZ = 42%, DZ = 9%
(Grade 2 – MZ = 12%, DZ = 9%; Grade 3 – MZ =25%, DZ = 27%)
Conclusion:
Genes appear to play an important role in schizophrenia because the concordance rate is higher in MZ twins than DZ twins. However environmental factors must also be important as the concordance is not 100%.
Evaluation:
Generalisability:
A large sample was used including different ages and both male and female patients meaning the findings could be generalised. However as the sample only focused on twins this means the findings may only be generalised to twins. Also only one hospital was used.
Reliability:
Sampling was carefully controlled using multiple measures to make sure that twins were correctly allocated either MZ or DZ twin status, and a lot of data was gathered using multiple research methods to check the diagnoses were correct. However interviews and self report data may be less reliable.
Application:
If there is a genetic component for Schizophrenia this is useful because it can help lead to identifying specific genes.
Other evaluation points:
Other studies support findings of MZs sharing traits – Bailey (2000) concordance rates for homosexuality – MZs 24% females, 20% males these figures were much lower for DZ twins
If schizophrenia was entirely a product of genes the concordance rates for MZs would be 100% - this is not the case so environmental factors must play a role
Twins may be treated the same or may copy each other, therefore higher concordance due to environmental rather than biological factors
The study did not look at reasons for schizophrenia or forms of schizophrenia therefore it is limited in its use – it simply identifies a concordance between schizophrenia and genes