Biological Explanations for Schizophrenia

• Family Studies: Strong relationship between the degree of genetic similarity and shared risk of schizophrenia
• Gottesman (1991): Conducted a large scale study found in an example that someone with an aunt with schizophrenia has a 2% chance of developing it, 9% for a sibling and 48% for an identical twin.
• Candidate Genes: Early research on candidate genes looked unsuccessfully for a single genetic variation to explain schizophrenia.
• • Schizophrenia is polygenic - it requires several genes.
  • It is aetiologically heterogeneous - the risk of schizophrenia is affected by different combinations.
• Ripke et al (2014): combined all previous data from genome-wide studies. They found that 108 separate genes were associated with a slightly increased risk of schizophrenia.
• Mutation:

  • Schizophrenia can also have a genetic origin in the absence of a family history due to the mutation in parental DNA.
  • Evidence comes from the correlation between paternal age (associated with the risk of sperm mutation) and risk of schizophrenia (Brown et al 2002)
• Role of Dopamine: Dopamine is widely believed to be involved in schizophrenia because it is featured in the functioning of brain systems which are related to the symptoms of schizophrenia.
• High dopamine activity in the subcortex (central areas of the brain) are associated with hallucinations and speech poverty.

  (hypodopaminerga e.g. excess dopamine receptors in pathways linking from subcortex to Broca's Area)
• Low levels of dopamine in the prefrontal cortex (responsible for thinking) could explain negative symptoms.
• Howes et al: The Prefrontal Cortex explains origins of abnormal dopamine - genetic variations and early experiences of stress cause some people to be more sensitive to Cortical Hypodopaminerga, and therefore sensitive to Subcortical Hyperdopaminerga.
• Strength - Strong Evidence Base

  • Gottesman family studies show risk of schizo. increases with genetic similarity - twin study found 33% concordance for MZ (monozygotic) and 7% DZ (dizygotic) twins
  • Adoption studies (Tienari et al 2004) show biological children of parents with schizophrenia were at a greater risk even if they grew up in an adoptive environment.
  • Shows some are more vulnerable to schizophrenia due to genes
• Limitation - Evidence for environmental risk factors

  • Biological risk factors include birth complications (Morgan et al 2017) and smoking THC-rich cannabis in teenage years (Di-Forti et al 2015)
  • Psychological risk factors include childhood trauma - 67% of people with schizophrenia reported at least one childhood trauma.
  • This means genes alone cannot provide a complete explanation for schizophrenia.