Biological: explaining OCD

• Genetic explanations for OCD

  • Candidate genes
  • OCD is polygenic
• Genetic explanations: candidate genes

  • There are specific gene markers that make people vulnerable to developing OCD.
  • Some genes involve the serotonin system e.g. SERT gene which is linked to lower levels of the neurotransmitter serotonin
• Genetic explanations: OCD is polygenic

  • 230 different genes may be involved in OCD development
• Genetic explanations of OCD: Strength - supporting evidence

  • Family studies demonstrate that the disorder is more common among first degree relatives (e.g. parents or siblings) of affected individuals. 10% of these relatives have the disorder, compared to 2% of the general population. This suggests a genetic component.
  • Twin studies - Nestadt et al reviewed previous twin studies and found a concordance rate of 68% for MZ twins comapred with 31% for DZ twins. This strongly indicates a genetic influence on OCD, however concordance rates may reflect the shared environments.
• Genetic explanations: weakness - environmental risk factors

  • Environmental risk factors can trigger or increase the risk of developing OCD. Cromer et al found that over half of OCD patients in their sample had experienced a traumatic event in their past and that the OCD was more severe in those who had experienced more than one trauma.
  • This suggests OCD cannot be entirely genetic in origin.
• What are the two explanations for OCD?

  Neural explanations, Genetic explanations
• 2. Neural explanations

  • The role of serotonin: OCD is linked with low levels of the neurotransmitter serotonin. Serotonin regulates mood. Low levels of serotonin prevent normal transmission of mood-relevant information from neuron to neuron.
• 2. Neural explanations

  • brain structure: the basal ganglia system and others has been implicated - communication within these areas is disturbed and might account for the repetitive behaviours seen in OCD.
• Neural explanations - strength

  • Supporting evidence (for both role of serotonin/basal ganglia)
  • Role of serotonin: drugs which increase levels of serotonin are effective in reducing OCD symptoms
  • Role of basal ganglia: DBS (deep brain stimulation) that targets loops in the basal ganglia has been effective at reducing symptoms.
  • This suggests that the serotonin system and the basal ganglia are both involved in OCD.
• Neural explanations: limitation

  • People with OCD do have abnormalities in neurotransmitter levels and brain structures.
  • However, these biological abnormalities could be the result of OCD, not a cause of it.
  • This means serotonin levels and particular brain structures are not necessarily a clear cause of OCD