genetic factors

• Twin Studies: Gottesman & Shields (1966)


  In 1991, they concluded from a meta analysis of 40 studies that concordance rates were:

  • 48% risk for MZ twins
  • 17% risk for DZ twins
• issues with twin studies

  difficult to eliminate environmental factors
• twins reared apart

  Gottesman (1982) found that 58% of twins reared apart (7/12 pairs) were concordant for schizophrenia
• Cardno (1999)


  found a 40% concordance rate between MZ twins reared apart compared to 5.3% in DZ twins reared apart
• evaluation of twins reared apart

  • often aren't separated at birth
  • sample sizes are small
  • may still have been raised by members of the same family
  • still shared uterine environment
  • could be a biological factor, but may not be genetic
• the Copenhagen high risk study

  • prospective study
  • compared 207 children w/ schizophrenic (high risk) mothers and 104 control children with health mothers (low risk)
  • children aged 10 & 18 at the start of study showed no symptoms and were treated over a number of years
• the Copenhagen study: Findings

  • 16.2% of high risk group were diagnosed with schizophrenia
  • 1.9% of low risk group was diagnosed with schizophrenia
  • schizophrenia personality disorder and other mental disorder were diagnosed on 18.8% of high risk group compared to 5% of low risk group
• the Copenhagen study: Evaluation

  STRENGTHS:

  • prospective study
  • large sample used

  WEAKNESSES:

  • culturally biased
  • some mothers in high risk sample may have been misdiagnosed
• Tienari et al 


  found that out of 164 adopted children whose mothers had been diagnosed with schizophrenia, 6.7% of children also shared this diagnosis compared to only 2% out of 197 children with non-schizophrenic mothers. This supported the role of genes influencing the onset of schizophrenia.
• Joseph (2004)


  found that when comparing identical twin studies, they had a concordance rate of 40% while non-identical twins had 7.4%.

  
  

  This higher concordance rate would present a strong argument for genetic factors.
• The Finnish adoption study- Tienari (1969)

  • Study identified 112 cases of ‘adopted out’ children who had been born to schizophrenic mothers and compared them against 135 control children​
  • 7% of the schizophrenic group developed the illness, compared with just 1.5% of the control group
• issues with adoption studies


  • Individuals who adopt children with schizophrenia will be told the background of the child. ​which may cause them to treat them as if they already have schizophrenic symptoms