AO3

• A strength is that there is a strong evidence base for the genetic basis of schizophrenia. Family studies show risk increases with genetic similarities. A twin study found 33% concordance rate for monozygotic and 7% for dizygotic twins. Adoption studies show that biological children of parents with schizophrenia are at greater risk even if they grow up in an adoptive family. This shows that some people are more vulnerable to schizophrenia because of their genes.
• A limitation is that there is evidence for environmental risk factors. Biological risk factors include birth complications and smoking cannabis in teenagers. Psychological risk factors include childhood trauma. For example, 67% with schizophrenia reported at least one childhood trauma. This means that genes alone cannot provide a complete explanation for schizophrenia.
• A strength is that there is real-life application in genetic counselling. If potential parents have a relative with schizophrenia, they can be advised of the risk of having a child with the condition. However, the risk estimate is just an average figure based on genetic similarity to relatives and does not take account of the future child's environment. This means that genetic counselling may only provide a crude idea of vulnerability and is of limited use.
• A strength is that Tenn et al. was able to induce schizophrenia-like symptoms in rats using amphetamines to raise dopamine, then relieve the symptoms using drugs that reduce dopamine. However, apomorphine also increases dopamine, but with none of the schizophrenia-like symptoms, and amphetamine psychosis is not the same as schizophrenia. This means that there is probably not a strong enough link between dopamine and schizophrenia.
• A limitation is that there is evidence for a role of glutamate. Post-mortem and scanning studies found raised glutamate in people with schizophrenia. Also, several candidate genes for schizophrenia are believed to be involved in glutamate production or processing. This means that a strong case can be made for other neurotransmitters in schizophrenia.