AO3 OCD biological explanations

• Evidence from family and twin studies

  Evidence for the genetic basis of OCD comes from studies of relatives and twins.

  • Nedstadt et Al (2000) identified 80 patients with OCD and 343 of first degree relatives compared with 73 control patients (no mental disorders) and 300 of their relatives.
  • First degree relatives of those with OCD were 5x more at risk of developing OCD
  • a meta-analysis of 14 OCD twin studies found MZ twins are more likely to develop OCD than DZ.
  • But, concordance rates aren't 100% other factors play a role in OCD developing
  • Supporting the diathesis-stress model.
• Research support for the role of the OFC


  Many studies support the genetic link to abnormal levels of neurotransmitters

  • Menzies et Al used MRIs to produce images of OCD patients and their brain 🧠 activity compared to their family members without OCD and unrelated healthy people.
  • OCS patients & relatives had reduced grey matter in key regions of the brain 😔 including the OFC

  Supports the view that anatomical differences are inherited and these may lead to OCD in certain individuals. Menzies et Al concluded brain scans can be used to detect OCD risk in the future
• Support from Tourette's syndrome and other disorders 


  Evidence of the role of genes in OCD comes from studies of people with other disorders.

  • Pauls and Leckman studied Tourette's patients & concluded that OCD is one form of expression of the same gene 🧬 that determines Tourette's. The obsessive behaviour in OCD and Tourette's found in autistic & anorexic patients.
  • It was reported that 213 patients with OCD also expressed at least one episode of depression
  • Supporting the view that there isn't a specific gene/s for OCD, but one that acts as a predisposition for obsessive behaviour
• Real-world application

  The mapping of the human genome had lead to the hope that specific genes could be linked to particular mental and physical disorders.

  • For example, if a future parent has COMT gene variation their eggs can be screened.
  • This gives parents choice to abort the eggs with the mental illness prone gene
  • Also, gene therapy may produce a means of turning certain genes "off" so disorders aren't expressed.
  • Both these can be beneficial, but raise ethical issues.
  • Showing that genetic therapy is more complex and controversial than first thought 🤔