Genetic explanation 5

• Szatamari (1991)

  Combined data from several studies to calculate overall sibling risk.

  This showed the proportion of siblings of people diagnosed with ASD, that also meet the criteria. The rate was 2.2%.

  For someone without siblings with ASD it’s 0.11%.

  20x greater risk of ASD if your sibling has it.
• Bailey et al 1995

  Analysed data from the British twin study.

  The concordance rate for MZ twins was 60% & for DZ twins was 0%.

  Researchers then widened the definition of autistic behaviours to include other characteristics as well as social impairment and found 92% concordance rate for MZ & 10% for DZ.
• Ritvo et al 1985

  Found concordance rates of 96% for MZ twins & 23% for DZ twins.
• Simplex families

  Families with only one member with ASD.

  ASD is likely caused by a de novo mutation.

  De novo mutation - a genetic alteration that is present for the first time as a result of a variant (or mutation) in a germ cell (egg or sperm) of one of the parents, or a variant that arises in the fertilized egg itself during early embryogenesis.
• Multiplex families

  More than one family member diagnosed with ASD or multiple members with autistic traits but not yet diagnosed.

  ASD likely caused by a genetic variation that is inherited.
• Strengths of the genetic explanation

  Supporting evidence

  Scientific

  Deterministic

  Reductionist
• Weaknesses of genetic explanation

  Counter evidence (lacks temporal validity)

  Difficult to distinguish between nature & nurture

  Deterministic

  Reductionist