A01

• Gottesman revealed that the greater genetic similarity between family members, the greater the likelihood of both developing schizophrenia. For example, the concordance rate (sharing similar traits) for schizophrenia in identical twins (100% genetic similarity) is 50%, compared to the concordance rate with schizophrenic parents (50% genetic similarity), which is 9%.
• There is no single candidate gene which is associated with an increased risk of developing schizophrenia. Instead, schizophrenia is polygenic, meaning that multiple genes work in combination. Schizophrenia is also aetiologically heterogeneous; different combinations of factors can lead to the condition. In fact, over 108 genetic variations have been found to be associated with increased risk of schizophrenia.
• Most of these genes are responsible for the functioning of neurotransmitters, most notably dopamine, leading to the dopamine hypothesis. The original version highlights hyperdopaminergia in the subcortex, for example excess dopamine receptors in Broca’s area have been linked to auditory hallucinations. The more recent version emphasises hypodopaminergia in the cortex, with low levels of dopamine in the prefrontal cortex associated with negative symptoms.