Genetic

• The assumption of the genetic explanation of schizophrenia is hereditary and runs in the families.
• The genetic basis of schizophrenia has been measured through family studies. Family studies have found that the closer the relationship to someone with schizophrenia genetic-wise, the higher the risk for an individual to develop schizophrenia.

  Genetic similarity

  [1st cousins: 2%, Other siblings:9%, Identical twins:48%]
• However, a problem with family studies is family members tend to share aspects of their environment as well as genes, therefore difficult to establish direct influence of genes alone - may lack validity
• Other research from twin studies investigate concordance rates

  Monozygotic twins share 100% of genes should have higher concordance rates compared to dizygotic who share 50%.
• Twin studies have found:

  • Torry et al(1994) found it one monozygotic twins develops schizophrenia, 28% chance that the other twin will.
  • Gottesman & Shield(1976): reviewed 5 twin studies concordance rates are never 100%
• However, a problem with using MZ and DZ twins is that concordance rates are never 100% in MZ twins. Twins off in same environment so effects of nature vs nurture unseen.
• Adoption studies aim to separate out issues of genes and environment. Kety and Ingraham (1992) found prevalence rates of schizophrenia are 10 times higher among genetic relatives than adoptive relatives of schizophrenia.
• Candidate genes are individual genes believed to be associated with the risk of inheriting schizophrenia
• Schizophrenia is polygenic. This means that there are a number of genes, each giving an increased risk of schizophrenia.

  108 separate genetic variations associated with schizophrenia

  Different studies have found different combinations of genes as an influence on schizophrenia.