Biological approach to explaining OCD - genetic and neural

• Genetic Explanation 1: The COMPT gene

  • The COMT gene may contribute to OCD
  • COMT regulates the production of dopamine – which is a neurotransmitter linked to OCD (dopamine levels are high in people with OCD)
  • All genes come in different forms (alleles)
  • One form of the COMT gene has been found to be more common in OCD patients than those without OCD
  • This variation of the COMT gene produces higher levels of dopamine which then leads to OCD.
• Genetic Explanation 2: The SERT gene

  • The SERT gene affects the transport of the neurotransmitter serotonin
  • A mutation in the SERT gene creates lower amounts of serotonin.
  • Lower levels of serotonin are associated with OCD
  • One study found a mutation of this gene in two unrelated families where 6 of the 7 members had OCD (Ozaki et al., 2003)
• Neural Explanation 1: Serotonin and Dopamine

  • Dopamine levels are abnormally high in people with OCD
  • Animal studies show that high doses of drugs that enhance levels of dopamine induce movements resembling compulsive behaviours found in OCD patients (Szechtman et al. 1998)
  • Lower levels of serotonin associated with OCD – because serotonin affects mood
  • Antidepressant drugs that increase serotonin activity reduce OCD symptoms (Pigott et al 1990)
• Neural Explanation 2: Decision Making Systems

  • Some cases of OCD are linked to impaired decision making
  • This in turn may be associated with abnormal functioning of the lateral (side bits) of the frontal lobes of the brain
  • The frontal lobes are the front part of the brain (behind your forehead) that are responsible for logical thinking and making decisions
  • There is also evidence to suggest that an area called the left parahippocampal gyrus (associated with processing unpleasant emotions) functions abnormally in OCD.
• Diathesis-Stress Explanation

  • It is unlikely that there is a simple link between a specific gene and a complex disorder like OCD
  • Genes like SERT are also linked to a number of other disorders like depression and PTSD
  • The diathesis-stress model suggests that each individual gene only creates a vulnerability for OCD, as well as other conditions such as depression
• Diathesis stress explanation :

  • Other factors such as the environment/situation determine whether any mental illness actually develops as a result of this gene
  • Therefore, some people could possess the COMT or SERT gene variations but not suffer from mental illness
• AO3:

  • The role of genetic factors is supported by family studies of OCD
  • For example, Nestadt et al. (2000) found that people with a first degree relative with OCD are more at risk of developing the disorder
  • They found that people with OCD had a five-times greater risk of having the illness themselves at some point in their lives, compared to the general population
  • However, families typically share the same environments as well sharing genes
  • This means that environmental factors could also play a part in the development of OCD (the stress diathesis model)
• AO3:

  • Additional support for the role of genetic factors in OCD comes from twin studies
  • For example, in their meta-analysis, Billet et al. (1998) found a higher concordance rate for OCD in MZ than DZ twins
  • They found that, on average, MZ twins were more than twice as likely to develop OCD if their co-twin had the disorder compared to DZ twins
  • However, the concordance rate for MZ twins is never 100%
  • This means that environmental factors must also play a role in OCD
• AO3:

  • A limitation of the biological explanation of OCD is that it ignores important psychological factors
  • For example, the two-process model suggests that OCD may be caused by an association between a neutral stimulus (e.g. dirt) and anxiety (classical conditioning)
  • It also suggests that this association is maintained through operant conditioning because the stimulus causing anxiety (dirt) is avoided through compulsive behaviours (hand-washing)
  • Therefore, is important to also consider psychological causes of OCD as well as biological causes
• AO3:

  • A strength of research into the biological explanation of OCD is that it has led to the hope that specific genes could be linked to particular mental and physical disorders
  • For example, where a parent-to-be has the COMT gene, the mother’s fertilised egg can be screened
  • Gene therapy may produce a means of turning certain genes ‘off’ so that a disorder, such as OCD, isn’t expressed
  • This could help to prevent mental disorders such as OCD
  • However, this does raise ethical issues