Genetic Factors

• Mutations in Sperm


  Can occur due to radiation, poison or viral infection
• Paternal age (associated with increased risk of sperm mutation)

  Increases risk of schizophrenia, from around 0.7% with fathers under 25 to over 2% in fathers over 50
• Twin studies


  • Assumed the greater concordance for schizophrenia between monozygotic twins is a result of greater genetic similarity rather than the greater environmental similarity
  • Monozygotic twins are treated more similarly, encounter more similar environments and experience more identity confusion than dizygotic twins
• Gottesman's family study


  1. Determined whether biological relatives of individuals with schizophrenia are similarly affected more often than non-biological relatives

  2. Monozygotic twins concordance rates were 48% vs dizygotic twins with 17% and children with 13%

  3. Shows genetic link but not 100%
• Tienari's adoption study in Finland


  1. Of the 164 adoptees whose biological mothers had been diagnosed with schizophrenia, 6.7% also had schizophrenia compared to just 2% of the 197 control adoptees born to non-schizophrenic mothers

  2. Concluded the 'genetic liability to schizophrenia had been confirmed'

  3. Better than twin studies as brought up in different environments so can separate nature from nurture
• Schizophrenia can occur even in the absence of a family history of the disorder
• One explanation for this is mutation in parental DNA, for example in paternal sperm cells
• Genetic factors play a role in schizophrenia