Biological approach to explaining OCD

Genetic explanations

Genes are involved in individual vulnerability to OCD. Lewis(1936) observed that 37% of his OCD patients had parents with OCD and 21% had siblings with OCD. This suggests that OCD runs in families, although what is passed on through generations is genetic vulnerability, not the certainty of OCD

The diathesis stress model

The diathesis stress model states that certain genes leave some people more likely to develop a mental disorder but it is not certain. Some environmental stress (experience) is necessary to trigger the condition

Candidate genes

Candidate genes create vulnerability for OCD. Some of these genes are involved in regulating the development of the serotonin system. Examples are

• COMT gene - variation of this gene results in higher dopamine levels

• SERT gene - affects the transport of the neurotransmitter serotonin

OCD is polygenic

This means that OCD is not caused by one single gene but by a combination of genetic variations that together increase vulnerability

Different types of OCD

One group of genes may cause OCD in one person but a different group of genes may cause OCD in another person - this is called aetiology heterogeneous

Evaluation

• One strength is that it is biased on strong evidence - Gerald Nastadt(2010) reviewed twin studies and found that 68% of identical twins share OCD , as opposed to 31% non-identical twins. Other research has found that a person with a family member diagnosed with OCD is around 4 times more likely to develop it that someone without an OCD family member

• One limitation is that there are environmental risk factors - there is strong evidence for the idea that genetic variation can make a person more or less vulnerable to OCD. However, OCD does not appear to be entirely genetic in origin and it seems that environmental risk factors can also trigger or increase the risk of developing OCD. Cromer (2007) found that over half of her OCD clients had experienced a traumatic event - NATURE

Neural explanations

The role of serotonin - serotonin is believed to help regulate mood. Neurotransmitters are responsible for relaying information from one neuron to another. If a person has low levels of serotonin, normal transmitters of mood-relevant information does not take place and the person may experience low moods

Decision-making systems - in some cases of OCD, it is associated with decision-making. For example, abnormal functioning of the lateral of the front lobes (responsible for logical thinking and decision-making) or the parahippocampal gyrus which is associated with unpleasant emotions

Evaluation

• one strength is the existence of supporting evidence - antidepressants that work purely on serotonin are effective in reducing OCD symptoms and this suggests that serotonin may be involved in OCD. This suggests that biological factors may also be responsible for OCD

• One limitation is the serotonin-OCD link may not be unique to OCD - many people with OCD also experience clinical depression. Having 2 disorders together is called co-morbility. This depression involves disruption to the action of serotonin with leaves us with a logical problem when it comes to serotonin as a possible basis for OCD