Biological explanations for schizophrenia

• Two main biological explanations for schizophrenia

  • Genetics
  • Neural correlates: The dopamine hypothesis
• Genetics

  • The genetic basis of schizophrenia has been investigated using family studies and studies of individual genes
• Family studies

  1. Schizophrenia is more common among the biological relatives of an individual with schizophrenia

  2. The greater the degree of genetic relatedness, the greater the risk
• Family studies

  • Individuals with an identical twin (100% of genes shared) who suffers from schizophrenia have a 48% risk of being diagnosed with the disorder
  • Individuals with a sibling (approximately 50% of genes shared) who suffers from schizophrenia have a 9% risk of being diagnosed with the disorder
  • The general risk of being diagnosed with the disorder is just 1%
• Studies of individual genes

  • There are a number of genes that have been related to schizophrenia (called candidate genes)
  • Schizophrenia is polygenic (unlikely to be related to a single gene)
  • Schizophrenia is aetiologically heterogeneous (different combinations of genes can lead to the condition)
  • Ripke et al. (2014) found that 108 separate genetic variations were associated with an increased risk of schizophrenia
• Neural correlates of schizophrenia

  • There are specific abnormalities within the brain that have been associated with the development of schizophrenia
• Dopamine hypothesis

  • Dopamine is one of the neurotransmitters involved with schizophrenia
  • The original version focused on the association between high levels of dopamine activity (hyperdopaminergia) in the subcortex and the positive symptoms of schizophrenia
  • More recent versions have also focused on the association between low levels of dopamine activity (hypodopaminergic) in the cortex and the negative symptoms of schizophrenia