Genetic AO3

• Lewis et al. observed that of his OCD patients, 37% had parents with OCD and 21% had siblings with OCD
• Nestadt found that people with first degree relatives (parents, offspring, sibling) with OCD were 5 times more likely to develop OCD compared to the rest of the population
• Twin studies can be used to investigate the genetic basis of behavioural traits
• Nestadt reviewed previous twin studies of OCD and found that 68% if identical twins compared to 31% of non-identical twins share concordance
• Nestadt’s review of twin studies suggests that there is a genetic basis for this disease because monozygotic twins share 100% of their genes with each other, whilst dizygotic twins only share 50% of genes with each other.
• What is a limitation of twin studies?

  Concordance rate is never 100% and environmental factors must play a role in development of OCD therefore genes can’t fully explain OCD. Twins most likely grew up in similar environments and upbringing. They may also replicate OCD behaviours (social learning theory). Therefore, findings can’t be generalised to the wider population and lacks population validity (only 3% are twins)
• What is the diathesis stress model?


  Genes create inherited vulnerabilities for OCD development but stressors in our environment determine whether the illness develops. Some people may have COMT + SERT gene but don’t have OCD
• Explanation supported by twin studies is scientific and DNA mapping technology is valid evidence