OCD

• What is the cycle of OCD?

  An obsessive thought will trigger anxiety, leading to the individual performing compulsive behaviour giving them a temporary relief from their anxiety. Once they have obsessive thoughts again, the cycle repeats.
• What is the genetic explanation to OCD?

  • OCD is not genetic itself but genetics can cause people to have a predisposition (vulnerability) to OCD
  • Lewis observed that 37% of OCD patients have OCD parents and 27% have OCD siblings, suggesting that the vulnerability is inherited but NOT the OCD itself
  • Diathesis-stress model: certain genes leave people more likely to develop a mental disorder but can only be triggered by some environmental stress
• What are candidate genes?

  • Genes that cause vulnerability for OCD
  • Some of these are involved in regulating serotonin or the transport of serotonin across synapses
• What do we mean by polygenic?

  • A combination of genetic variations that together significantly increase vulnerability for OCD rather than a single gene
  • Taylor (2013) - found that up to 230 different genes may be involved in OCD
• Why are there different types of OCD?

  • OCD is aetiologically heterogeneous: the origins of OCD vary from one person to another
  • Different types may be the result of particular genetic variations
• What is the COMT gene?

  • Regulates the production of the neurotransmitter dopamine (mood, satisfaction, sleep)
  • A mutation of the COMT gene reduces its' ability to break down dopamine, leading to higher levels of dopamine in the brain and overactivity in areas like the prefrontal cortex
  • People with OCD have very high dopamine levels
• What research support is there for the COMT gene's association with OCD?

  • Turk et al. found that a variation of the COMT gene leads to lower levels of the COMT gene's activity -> leading to higher dopamine levels
  • Found that it is more common amongst people with OCD than clinically normal people providing evidence that OCD has a genetic basis
• What is the SERT (5-HTT) gene?

  • Affects the transport of serotonin across synapses in the brain, a mutation leads to lower levels of serotonin
  • Found amongst OCD patients - can be more hyperaware of their environments than usual
• What research support is there linking the SERT gene mutation to OCD?

  • Ozaki et al (2003) - found SERT gene mutation in 2 unrelated families where 6/7 family members had OCD
  • Supports genetic explanation of OCD as it shows a positive correlation between the diagnosis of OCD and the presence of a specific mutation of the SERT gene
  • Shows it can be hereditary/inherited
• What research support is there for the genetic explanation of OCD?

  • Nestadt et al. (2010) reviewed twin studies - 68% of identical (monozygotic) twins shared OCD as opposed to 31% of non-identical (dizygotic) twins
  • Stebnicki - someone with a family member with OCD is 4x more likely to develop it as someone without
  • Suggests there must be some genetic influence on the development of OCD
• What is a weakness of the genetic explanation of OCD?

  • OCD is not entirely genetic at origin - environmental factors can also trigger or increase the risk of developing OCD
  • Cromer et al. - over half OCD clients in their sample experienced a traumatic event in their past and their OCD was more severe
  • Means the genetic explanation is only partial
• What is the role of serotonin in OCD?

  • Serotonin is a neurotransmitter (responsible for relaying information from one neuron to another)
  • Low levels of serotonin means normal transmission of mood-relevant information does not take place and a person may experience low moods
  • Means some OCD cases may be explained by a reduction in the functioning of serotonin in the brain
• What research evidence is there for the role of serotonin in OCD?

  • Piggot et al: anti-depressant drugs like SSRIs (that increase serotonin activity) are effective in reducing OCD symptoms
  • Jenicke: anti-depressants that don't have a strong effect on serotonin do not reduce OCD symptoms
• What is the para-hippocampal gyrus and how is it associated with OCD?

  • Associated with processing unpleasant emotions and functions abnormally in OCD
  • Can cause difficulty distinguishing real threats from perceived threats
  • Can intensify the fear and anxiety produced by obsessions by abnormal connections with the amydgala