BA exp OCD

• Genetic exp. of OCD- Lewis (1936)

  • Observed that 37% of his OCD patients had parents with OCD
  • 21% had siblings with OCD
  • Suggests genes are involved with individual vulnerability and OCD runs in families
• OCD is polygenic- Taylor (2013)

  • Analysed findings of previous studies
  • found evidence of up to 230 genes involved in OCD
  • Genes have been associated with action of dopamine/serotonin, neurotransmitters involved with mood regulation
• Supporting evidence for genes in OCD- Nestadt et al

  • Reviewed previous twin studies
  • 68% of identical twins shared OCD
  • 31% of non-identical twins
  • Strongly suggests genetic influence
• Support for diathesis stress model/environmental risks in OCD- Cromer et al

  • Over 1/2 of OCD patients in sample had a traumatic event in their past
  • OCD more severe in those with more than one trauma
  • Therefore OCD cannot be entirely genetic, environment may stress symptoms
• What is the genetic explanation of OCD?

  • Genes are involved in individual vulnerability to OCD (evidence from Lewis 1936)
  • OCD runs in families and is likely genetic
  • OCD has candidate genes
  • OCD is polygenic
  • OCD is aetiologically heterogeneous
• What is a candidate gene that creates vulnerability for OCD?

  • 5HTI-D beta gene
  • Implicated in the efficiency of serotonin transport across synapses
• How many genes may be involved in OCD?

  • 230, found by Taylor et al
  • Many genes have been associated with action of dopamine and serotonin, involved in mood regulation
• What is the neural explanation for OCD?

  • The genes associated with OCD are likely to affect levels of key neurotransmitters which may trigger vulnerability
  • Low levels of serotonin may contribute to poor processing of mood-relevant information
• What is the role of serotonin in OCD? (neural explanation)

  • Low levels of serotonin may mean that mood-relevant information is not processed properly and other mental processes may be affected
  • A reduced functioning of the serotonin system may result in OCD vulnerability
• How do decision-making systems contribute to OCD vulnerability? (neural exp)

  • Abnormal functioning of the frontal lobe in the brain may lead to OCD (e.g. hoarding disorder may be linked to impaired decision making)
  • The left parahippocampal gyrus is linked to processing unpleasant emotions which may lead to faulty processing + OCD vulnerability
• What is a strength of the genetic explanation of OCD?

  • Good supporting evidence to suggest OCD has a genetic influence/basis
  • NESTADT et al
  • Reviewed twin studies, found 68% identical twins shared OCD
  • Opposed to 31% non identical twins
  • Strongly suggests OCD vulnerability has a genetic influence
• What is a limitation of the genetic explanation of OCD?

  • Too many candidate genes involved in the OCD vulnerability
  • There are up to 230 (Taylor et al) which each increase OCD vulnerability by a fraction
  • Therefore a limitation as genetic exp is unlikely to be useful as its reduced to predictive value
• What is a limitation of the genetic explanation due to environmental risk factors?

  • Environmental risk factors can also trigger/increase OCD vulnerability and development
  • The diathesis stress model
  • Cromer et al found that over 1/2 OCD patients had a traumatic event in their past
  • OCD was more severe with those who had multiple traumas
  • Therefore suggests OCD cannot be entirely genetic, environmental causes/stresses may also play a part
• What is a strength of the neural explanation of OCD?

  • Supporting evidence of neural mechanisms through the use of treatment for OCD
  • Use of antidepressants work on the serotonin system, reducing OCD symptoms
  • Suggests that serotonin system abnormalities may trigger OCD/involved in the development
• What is a limitation of the neural explanation?

  • It is unclear what exact neural mechanisms are involved
  • Cavedini found that neural systems involved in decision making have been the ones that function abnormally in OCD
  • However other research has found that other brain systems may be involved sometimes
  • No brain system has been found to always play a role, therefore explanation is incomplete and limits explanatory ability of OCD and neural links
• What is another limitation of the neural explanation (AO3)

  • Evidence to suggest various neurotransmitters and structures of the brain do not function normally
  • However these abnormal functioning do not cause OCD they may be a result
• Issue with twin study- Nestadt

  • Concordance rare for identical twins is not 100% (whilst their genes are) so may suggest environmental factors play a role.
  • DZ twins may have a less similar environment, and this may contribute to differences in concordance rates for OCD.
• Candidate genes linked to OCD vulnerability

  • 5HTI-D beta
  • COMT
  • SERT
• LEWIS (1936) observed that 37% of OCD patients had parents with OCD. 21% with OCD 
• RESEARCH SUPPORT NESTDAT TWIN STUDY

  • ->  empirical evidence to support the idea that OCD has a genetic basis.
  • Twin study, 68% identical twins (MZ) shared OCD vs 31% of non-identical twins (DZ)
  • Strongly suggesting OCD has a genetic basis/is inherited.
• Significance of SERT gene

  • Results in lower levels of serotonin
  • Results in malfunctioning to the caudate nucleus and orbitofrontal cortex
  • Leads to overwhelming feeling from anxiety
  • May lead to compulsions to relieve this
• Significance of COMT gene

  • Results in higher levels of dopamine
  • Can't suppress intrusive thoughts
  • Habit formation, compulsions are ingrained
  • Increases importance of intrusive thoughts