biological explanations for schizophrenia

• A strong relationship between the degree of genetic similarity and shared risk of schizophrenia. Gottesman's large-scale study found those with an aunt with schizophrenia has a 2% chance of developing it, 9% for a sibling and 48% for an identical twin
• Schizophrenia is polygenic which means that it requires several genes. Also, early research looked unsuccessfully for a single genetic variation to explain schizophrenia
• Schizophrenia can also have a genetic origin in the absence of a family history because of mutation in parental DNA. The evidence of this comes from the correlation between parental age and risk of schizophrenia
• Dopamine is featured in the functioning of brain systems related ti the symptoms of schizophrenia. High dopamine activity in subcortex associated with hallucinations and poverty of speech. Low levels of dopamine in the prefrontal cortex could explain negative symptoms. Genetic variations and early experiences of stress make some people more sensitive to cortical hypodopaminergia
• One strength of biological explanations is it has strong evidence. Family studies (e.g. Gottesman) show risk increases with genetic similarity. Twin study found 33% concordance for monozygotic twins 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.
• One limitation of biological explanations is evidence for environmental risk factors. Biological risk factors include birth complications and smoking cannabis in teenage years. Psychological risk factor include childhood trauma e.g. 67% with schizophrenia reported at least one childhood trauma. This means genes alone cannot provide a complete explanation for schizophrenia.
• One strength is support for dopamine in the symptoms of schizophrenia. Amphetamines increase dopamine and mimic symptoms. Antipsychotic drugs reduce dopamine and reduce intensity of symptoms. Candidate genes act on the production of dopamine or dopamine receptors. This strongly suggests that dopamine is involves in the symptoms of schizophrenia.
• One limitation of dopamine is evidence for a central role for glutamate. Post-mortem and scanning studies found raised glutamate in people with schizophrenia. Also, several candidate genes for schizophrenia are believes to be involved in glutamate production or processing. This means that a strong case can be made for a role for other neurotransmitters in schizophrenia