Genetic predisposition

• Szatmari - Sibling risk


  Siblings of people with ASD meet the criteria for ASD 2.2% whereas those without siblings who have ASD is 0.11% - 20x greater
• Bailey - Concordance rate in twin studies


  When one of the twins had ASD (met a criteria) - MZ 60%, DZ 0%. Wider definition - MZ 92.5%, DZ 10%
• Multiplex ASD


  Genetic variations that are inherited, runs in family
• Simplex ASD


  10% of cases 'de novo'. New mutation DNA deleted or duplicated as ovum divides. Affects multiple genes. Older parents.
• Syndromic ASD


  Accompanied by other conditions that may have well-established genetic case (one gene). Behaviour overlap offer cues to genetic factors involved.
• Concordance rate in twin studies (Colvert)

  MZ 0.77-0.99, DZ 0.22-0.65. Estimated inheritance 56%-95% depending on measure used.
• Earlier diagnosis and more effective interventions

  Offer fuller understanding
• Twin studies can't rule out environmental factors
• Diathesis stress model


  ASD caused by interaction of genetic disposition with early insult to developing brain. Not genes alone.
• Could learn and reduce environmental factors
• Chemical exposure in early pregnancy - prenatal exposure
• Highly heterogeneous - many traits. Genes make more contribution to some traits than others - none to cause the disorder
• Benvenuto - 90% ASD caused by multiple genes interaction with another and environmental factors