Biological Explanations of OCD


Two Biological Explanations of OCD

1) Genetics:                         

  • Twin Studies.
  • Family.

2) Neural Explanations:

  • Chemical Imbalance- Neurotransmitters.
  • Neurophysiology- Brain Structure. 

Genetic explanation use concordance rates. These are the probability that a pair of individuals will botth develop a disorder, if one twin or member of the family already has it.

Family Studies

  • Family studies have shown that there is a genetic vulnerability for developing OCD. 
  • Nesdat found first degree relatives e.g. parents or siblings of OCD sufferers have a 12% chance of developing of OCD compared with 3% of first degree relatives of a control group without OCD.

Twin Studies

  • There are two types of twins. Identical twins (Monozygotic- MZ) and non identical twins (Dizygotic- DZ).
  • MZ twins share 100% of their genetics.
  • DZ twins share 50% of their genetics.
  • Gottesman said there was 87% concordance rate for MZ twins where one twin has OCD and  47% concordance rate for DZ twins where one twin has OCD.

Candidate Genes

  • Refer to the genes carrying OCD. It is a polygenetic which means more than one gene causes OCD.
  • It is believed that the SERT (serotonin) gene and the COMPT (dopamine) gene work together to cause OCD.


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