Biological explanations of OCD

• What does the biological approach to OCD believe?

  That mental disorders are similar to physical illnesses and caused by abnormal biological processes.
• What are the genetic factors of OCD?

  • Predisposition - increased likelihood of having OCD due to inherited genes
  • First degree relatives - immediate family such as parents, siblings and children
  • Candidate genes - genes that are identified as potentially causing a particular disease/illness due to previous knowledge
  • Aetiologically heterogenous - different types of OCD may have different genes/causes
  • Polygenic - there are several genes involved in OCD
• What are the neural mechanisms of OCD?

  • Dopamine - neurotransmitter that is associated with pleasure, reward, motivation and motor control
  • Serotonin - neurotransmitter responsible for regulating mood, digestion, sleep etc
• What is the genetic explanation of OCD?

  • Lewis observed of his OCD patients, 37% had parents with OCD & 21% had siblings with OCD. Shows individuals with familial history of OCD have vulnerability to develop it but this is not certain. Known as the diathesis stress model
  • SERT gene involved with efficiency of transmitting serotonin (low levels in OCD) across synapses
  • COMT gene affects regulation of dopamine (too much in OCD)
  • Taylor analysed findings of previous studies & found evidence that up to 230 genes may be involved. Genes involved said to be associated with serotonin & dopamine
• Evaluation point of BE of OCD: biologically determinist?

  • Does inheriting the COMT gene mean that you will have OCD?
  • Twin studies - concordance rate between monozygotic twins is not 100%, suggests other factors play a role
  • Better described as a 'genetic predisposition of vulnerability'
• Evaluation point of BE of OCD: empirical evidence

  • There is a lot of empirical evidence i.e. from family studies
  • High concordance levels suggest there is a genetic basis to OCD. However, families share same environment so might not be biological but environmental
• Evaluation point of BE of OCD: serotonin

  • Evidence supports that serotonin is involved in onset of OCD.
  • Antidepressants, which increase levels of serotonin, decrease symptoms of OCD
  • Hu compared serotonin levels in 169 OCD sufferers and 253 non-sufferers. He found lower levels of serotonin in OCD sufferers, supporting idea it could be linked to OCD
  • However, link could be due to co-morbidity. Many OCD sufferers become depressed and reduced serotonin levels are linked to cause of depression. So could be depression, not OCD.
• Evaluation point of BE of OCD: biologically reductionist

  Evidence proves environmental factors can can trigger OCD. Cromer found that over 50% of OCD patients had suffered a traumatic event in the past and that symptoms were more severe in those who had suffered multiple traumas. Diathesis stress model may be more holistic explanation than a genetic predisposition.
• What are concordance rates?


  The likelihood of a disorder being present in both individuals. If the rates increase with genetic similarity, a genetic basis for the disorder is suggested.