1. Biological explanation for OCD
4.1.4 Psychopathology:
The biological approach to explaining OCD: genetic and neural explanations

2. Learning Objectives
Understand the key terminology associated with the biological explanation of OCD.
Outline genetic factors involved in the development of OCD
Evaluate genetic factors involved in the development of OCD

3. What are twin studies?

4. Genetics
OCD (obsessive compulsive disorder) has been explained in a number of ways but the biological approach offers particularly useful suggestions as to how it is caused.
It has been proposed that there is a genetic component to OCD which predisposes some individuals to the illness.
The genetic explanation suggests that whether a person develops OCD is at least partly due to their genes. This may explain why patients often have other family members with OCD.

5. Genetics Getting to know the key terminology:
Some of the definitions have been done for you, your job is to fill in the rest of the definitions using your text book. Pg

6. Genetics
Bellodi et al (2001) claim that genetic factors play a role in the disorder. Using evidence from twin studies and family studies, they showed that close relatives are more likely to have the disorder than more distant relatives.
Mckeon and Murray- patients with OCD are morel likely to have first degree relatives who suffer from anxiety disorders.
Pauls et al- there is a much higher percentage of OCD sufferers in relatives of patients with OCD than in the control group without OCD.
What conclusion can we draw from this?

7. Genetic explanations
Candidate genes are ones which, through research, have been implicated in the development of OCD.
A possible candidate gene is the SERT gene which is involved in regulating serotonin, a neurotransmitter which facilitates message transfer across synapses.
Another possible candidate gene is the COMT gene – this regulates the production of dopamine
Dopamine effects motivation and drive

8. Genetic explanations
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, for example a bereavement.
OCD is thought to be polygenic – this means that its development is not determined by a single gene but a few (maybe as many as 230 genes) – this means that there is little predictive power from this explanation.

9. Evaluation of genetic explanations
Genetics
There is evidence to suggest there is a genetic component to the disorder. One of the best sources of evidence for the importance of genes is twin studies (Nestadt – 2010)
Family studies could also be used to explain environmental influences
Close relatives of OCD sufferers may have observed and imitated the behaviour (SLT)
It is difficult to untangle the effects of environment and genetic factors

10. Evaluation of genetic explanations
Candidate genes
Candidate genes are ones which, through research, have been implicated in the development of OCD.
There are too many genes involved
Psychologists have not been successful at pinning down all the genes involved
Each genetic variation only increases the risk of OCD by a fraction

11. Evaluation of genetic explanations
Environmental factors
Individuals may gain a vulnerability towards OCD through genes that is then triggered by an environmental stressor.
Cromer (2007) found that over half the OCD patients in their sample had a traumatic event in the past, and that OCD was more severe in those with more than one trauma.
This means that it may more productive to focus on environmental causes as it seems that not all OCD is entirely genetic in origin

12. Exam question
With reference to the study described above, what do the results seem to show about possible influences on the development of OCD?
[4 marks]

13. Mark Scheme