GENETIC EXPLANATION

• OCD is polygenic as more than one specific gene has been identified in the onset of OCD. 
• TAYLOR (2013) - carried out a meta-analysis, finding as many as 230 different genes implicated in developing OCD. 
• COMT gene  


  Helps to reduce the action of dopamine. The variation in the COMT gene decreases the amount of COMT available and therefore dopamine is not controlled leading to too much dopamine (associated with OCD)
• SERT gene


  This affects the transport of serotonin, creating lower levels of this neurotransmitter. Low levels of serotonin have been implicated with OCD.
• It is recognised however that not everyone in a given family gets OCD so there must be additional factors. The diathesis-stress model suggests that people gain a vulnerability towards OCD through genes, but an environmental stressor is also required. This could be a stressful event e.g., a bereavement. 
• NESTADT ET AL (2000)

  • 80 patients with OCD and 343 of their near relatives compared with control group without mental illness and their relatives. 
  • Strong link with near family --> 5x greater risk if had first degree relative. 
• BILLETT ET AL (1998)

  • Meta-analysis (a study containing the results of lots of studies) of 14 twin studies 
  • On average monozygotic (identical) twins are 2x more likely to develop the disorder than dizygotic (non-identical) twins. 
• OZAKI ET AL (2003)

  • Mutations of the SERT gene were found in two unrelated families where 6 of the 7 family members had OCD.