Explaining

• OCD is a condition that may be largely understood as biological in nature.
• What is the biological approach?

  A perspective that emphasises the importance of physical processes in the body like genetic inheritance and neural function
• What are the genetic explanations of OCD?

  That genes are involved in individual vulnerability to OCD.

  • Diathesis-stress model
  • candidate genes
  • polygenic
  • Aetiologically heterogenous
• What are genes?

  Make up chromosomes and consist of DNA which codes the physical features of an organism and psychological features.

  Genes are inherited
• What is the diathesis stress model?

  Certain genes leave some people more likely to develop a mental disorder but it isn’t certain.

  • Some environmental experience is necessary to trigger the condition
• Lewis (1936)

  • Observed that his 37% of his OCD patients had parents with OCD and 21% had siblings with OCD
  • Suggests that OCD runs in families
• What are candidate genes?

  Genes identified which create vulnerability for OCD.

  Some of these genes are involved in regulating the development of the serotonin system

  • E.g. the gene 5HT1-D beta is implicated in the transport of serotonin across synapses
• Taylor (2013)

  • Analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD
• What is polygenic?

  Not caused by 1 single gene but by a combination of genetic variations that together significantly increase vulnerability
• Genes studies in relation to OCD include those associated with the action of dopamine and serotonin

  • Both neurotransmitters are believed to have a role in regulating mood
• Aetiologically heterogenous?

  The origins of OCD vary from one person to another.

  One groups of genes may cause OCD in one person but a different group og genes may cause OCD in another person
• There’s some evidence suggesting that different types of OCD may be the result of particular genes

  • such as hoarding disorder and religious obsession
• Research support- A03

  Variety of sources strongly suggests some people are vulnerable to OCD due to their genes

  strong evidence base

  Nestadt et al. (2010)

  • reviewed twin studies
  • found 68% MZ twins shared OCD opposed to 31% DZ twins

  Marini and Stebnicki (2012)

  • family study
  • research found that someone with a family member diagnosed with OCD is 4 times more likely to develop it than someone without it

  suggest genetic influence on the development of OCD
• Animal studies- A03

  It’s hard to find candidate genes

  Animal studies suggest that particular genes are associated with repetitive behaviours in other species like mice
• Environmental risk factors- A03

  OCD doesnt appear to be entirely genetic in origin

  environmental risk factors can trigger OCD

  Cromer et al. (2007)

  • found over half of OCD clients in had experienced a traumatic event
  • OCD was more severe in those with 1 or more traumas

  Genetic vulnerability only provides a partial explanation for OCD
• Imitation- A03

  OCD may run in families due to social learning theory
• Candidate genes

  Researchers have identified specific genes which create a vulnerability for OCD

  • Serotonin genes like 5HT1-D beta, are implicated in the transmission of serotonin across synapses
  • Dopamine genes are implicated in OCD and may regulate mood

  Both dopamine and serotonin are neurotransmitters
• OCD is polygenic

  OCD isn’t caused by 1 single gene but several genes

  Taylor (2013)

  • found evidence that up to 230 different genes may be involved in OCD
• Aetiologically heterogeneous

  One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person

  There’s also evidence that different types of OCD may be the result of particular genetic variations like hoarding disorder and religious obsession
• Low levels of serotonin lowers mood

  Neurotransmitters are responsible for relaying information from 1 neuron to another

  • e.g. if someone has low levels of serotonin then normal transmission of mood relevant information doesn’t takes place and mood or mental processes are affected
• Decision-making systems in frontal lobes impaired

  Some cases of OCD like hoarding disorder are associated with impaired decision aking

  • may be associated with abnormal functioning of the lateral frontal lobes of the brain- which are responsible for logical thinking and making decisions
• Parahippocampal gyrus dysfunctional

  There’s evidence to suggests that the left parahippocampal gyrus which is associated with processing unpleasant emotions functions abnormally in OCD
• Supporting evidence of the neural model- A03

  Antidepressants that work on serotonin reduce OCD symptoms

  • suggests serotonin is involved in OCD

  Also OCD symptoms form part of conditions that are known to be biological in origin like Parkinson’s disease

  This means that biological factors are likely to be involved in OCD
• No unique neural system- A03

  Many people with OCD also experience depression

  • probably involves disruption to the action of serotonin

  Could simply be that the serotonin activity ois disrupted in many people with OCD because they’re also depressed.

  Means that serotonin may not be relevant to OCD symptoms
• Correlation and causation- A03

  Some neural systems don’t work normally in people with OCD

  • The biological model suggests this is explained by brain dysfunction causing the OCD

  But this is just a correlation which doesn’t necessarily indicate a causal relationship

  • OCD or depression might cause the abnormal brain function

  Means there’s a lack of strong evidence for a neural basis to OCD though correlations may eventually lead us to a cause