genetic explanations

• Genetic explanation

  There is no OCD gene; however, its thought a vulnerability or predisposition to OCD is inherited from parents.

  Genetic analysis has revealed around 230 separate 'candidate genes' found more frequently in people with OCD; many candidate genes influence the functioning of neural systems in the brain; e.g. the SERT gene affects reuptake in the serotonin system. Other identified genes include the COMT gene.
• Genetic explanation
- polygenic


  As so many candidate genes have been identified, this suggests OCD is polygenic, meaning a predisposition to OCD requires a range of genetic changes.
• COMT gene

  COMT regulates the production of dopamine. Tukel et al: One variation of the COMT gene results in higher levels of dopamine and this variation is more common in patients with OCD.
• SERT gene


  SERT affects the transportation of serotonin. This causes lower levels of serotonin, which is implicated in OCD. Ozaki et al: A mutation of the SERT gene was found in two unrelated families. In these families 6/7 of the members had OCD.
• Diathesis-stress model


  Each individual gene creates a vulnerability for OCD. Other factors (stressors) affect what condition develops or indeed whether any mental illness develops at all. Some people could possess the COMT and SERT gene variations but suffer no illness
• + Supporting evidence for the genetic basis of OCD


  E - Billett et al: A meta-analysis of 14 twin studies of OCD found that, on average, MZ twins were more that 2x as likely to develop OCD if their co-twin had the disorder than DZ twins.

  E - This shows that there is a link between genetics and the likelihood of having OCD.

  L - However, no twin study has found a concordance rate of 100% in identical twins, which means that biological factors are not the only factor contributing to OCD.
• /+ Diathesis stress model may be a more valid explanation


  E - Cromer: 54% of 265 participants with OCD reported at least one traumatic life event, and those with traumatic life events reported increased severity of OCD symptoms.

  E - This shows that there may be an environmental aspect of OCD, which shows that the diathesis stress model may be a better explanation.

  L - Therefore, the genetic explanation of OCD does not take into account any other factors which may interfere.