genetic

• A review of twin studies found that 68% of identical twins shared OCD compared to 31% of non-identical twins. This is supporting evidence for the idea that people have a genetic vulnerability to OCD.

  Another study by Nestadt et al (2000) found that people with first-degree relatives with OCD had five times greater risk of having OCD themselves at some point in their lives.
• Twin studies make the assumption that identical twins are only more similar than non-identical in terms of their genes. They overlook that identical twins may also be more similar in terms of shared environments.
• Therefore, it is difficult to separate environmental and genetic factors in twin studies. The fact that the concordance rates are never 100% means that environmental factors must play a role too.

  And so, the explanation may be too deterministic and lead to the assumption that a person with a specific combination of candidate genes will develop OCD when it may be a genetic vulnerability paired with an environmental stressor that causes OCD. Using the diathesis stress model may provide a more comprehensive explanation of OCD.
• Psychologists have not been very successful at determining which genes are involved in OCD. One reason for this is that it seems that each genetic variation only increases OCD risk by a fraction.

  With over 230 candidate genes involved, there are practical issues as it's difficult to assess which candidate genes have the greatest influence and so which genes drug treatments should target. As OCD is polygenic, it is not possible to identify a single gene that it a cause.

  This means that the genetic explanation is likely to have little predictive value in the future.
• Environmental factors can also trigger or increase the risk of developing OCD.

  For example, it has been found that over half of OCD patients in one study had a traumatic experience in their past, and that OCD was more severe in participants with more than one trauma.

  This suggests OCD is not entirely genetic in origin and it may be more productive to focus on environmental causes.
• A further weakness of the explanation is that it ignores other factors and is reductionist. For example, it does not take into account cognitions and learning.

  Some psychologists suggest that OCD may be learnt and maintained by conditioning where the stimulus is associated with anxiety and then is avoided which negatively reinforces their compulsions. This explanation is supported by the success of behavioural treatments for OCD such as Exposure and Response Prevention.

  This suggests that OCD may have psychological causes as well as biological causes.