Genetic

• Schizophrenia is thought to be polygenic (a product of the combined effect of a number of candidate genes)
• This is investigated through family, twin and adoption studies
• Family studies - have established that SZ is more common among biological relatives of a person with SZ, and the closer the degree of genetic relatedness, the greater the risk
• Family study example - Gottesman and Shield

  Children with two schizophrenic parents had a concordance rate of 46%, children with one schizophrenic parent had a rate of 13% and siblings 9%
• Family studies

  Common rearing patterns may explain family similarities. Research has shown that SZ runs in families but could be due to other factors. For example research on expressed emotion has shown that a negative emotional climate can lead to SZ
• Twin studies - if monozygotic twins are more concordant than dizygotic twins then this suggests that the greater similarity is due to genetic factors
• Twin studies example - Joseph

  Calculated that the meta analysis for studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and 7.4% for DZ

  Should be 100% for MZ twins if due to genetics alone
• Concordance rates in twin studies has never been 100% for SZ
• Twin studies

  Joseph points out that MZ twins encounter more similar environments and experience more identity confusion. May explain higher concordance rates
• Adoption studies - studies of genetic related individuals who have been reared apart are used
• Adoption study example - Tienari

  Did a study in Finland. Of the adoptees who's biological mother had SZ, 7% received a diagnosis of SZ compared to just 2% in the control group
• However adoptees were found to only have this increased risk if there was dysfunction in the family, suggesting an interaction between genetic vulnerability and environmental influences