Genetic basis

• What is the genetic explanation for schizophrenia?

  • Schizophrenia runs in families, allowing us to conclude it has a genetic basis
  • This can be evidenced by family studies, adoption studies, and candidate genes
• How do family studies support the genetic explanation?

  • Confirmed that the risk of schizophrenia increase in line with genetic similarity to a relative with the disorder
  • Gottesman (1991) conducted a large-scale family study where he found that someone with a schizophrenic identical twin has a 48% chance of developing it themselves, 9% for siblings, and 2% for aunts
  • Shows a positive correlation between genes and schizophrenia
• How do adoption studies support the genetic explanation?

  • Due to the difficulties of separating genetic and environmental influences of twin and family studies, genetically related individuals who have been reared apart are used
  • Tienari et al. (2000) found that 6.7% of 164 adoptees whose biological mothers were schizophrenic also received a diagnosis of schizophrenia compared to 2% of a control group
  • Investigators concluded from these findings that genetic liability to schizophrenia had been decisively confirmed
• What other aspects are there to the genetic explanation for schizophrenia?

  • Candidate genes put an individuals at higher risk of developing a disorder: Nucifora et al. (2012) found a link between mutations in the NPAS3 gene and schizophrenia
  • Polygenic: Ripke et al. (2014) found 108 separate genetic variations associated with increased risk of schizophrenia from genome wide studies
  • Aetiologically heterogenous: different combinations of factors, including genetic variations, can lead to the condition explaining different origins and sub-types
• What is one strength of the genetic explanation for schizophrenia?

  • Strong evidence base: family studies such as Gottesman show that risk increases with genetic similarity to a family member w/ schizophrenia. Adoption studies like Tienari et al. show that biological children of parents w/ schizophrenia are at heightened risk even if they grow up with an adoptive family, eliminating confounding variables like the environment
  • Hilker et al. (2018) showed a concordance rate of 33% for monozygotic identical twins and 7% for dizygotic non-identical twins, supporting the genetic basis for schizophrenia
• What is one limitation of the genetic explanation for schizophrenia?

  • Environmental factors: evidence shows that these can increase the risk of schizophrenia, including biological + psychological influences
  • Di Forti et al. (2015) found that smoking THC-rich cannabis in teenage years and birth complications can act as risk factors
  • Morkved et al. (2017) found that 67% of those with schizophrenia and related psychotic disorders experienced at least 1 childhood trauma as opposed to 38% of a matched group with non-psychotic issues
  • Means genetic factors alone cannot provide a complete explanation for schizophrenia
• What is another strength of the genetic explanation for schizophrenia?

  • Genetic counselling: acts as an application of our understanding of the role of genes in schizophrenia, and informs prospective parents of the probabilities of their child going on to develop schizophrenia by screening their genes
  • However, the risk estimate provided by this is just an average figure and can't pinpoint the probability due to not knowing what the child's environment will be like, therefore is not reliable for parents to base life-changing decisions on