The biological approach to explaining OCD

Candidate Genes

• Specific genes (candidate genes) have been identified which create a vulnerability for OCD
• Serotonin genes are implicated in the transmision of serotonin across synapses and dopamine genes are also implicated in OCD
• Both serotonin and dopamine are neurotransmitters that have a role in regulating mood

Polygenic disorder

• OCD is not caused by one particular gene, but rather a group of genes are involved
• Up to 230 genes may be involved in OCD (Taylor, 2013)

Different types of OCD

• OCD is aetiologically heterogenous- one group of genes may cause OCD in one person, but a different group of genes may cause OCD in another person
• Different types of OCD may be the result of particular genetic variations e.g. hoarding disorder and religious obsession

Good supporting evidence

• Evidence suggests that some people are vulnerable to OCD due to their genetic make-up
• Twin studies have shown that 68% of MZ twins shared OCD as opposed to 31% of DZ twins
• This strongly supports a genetic influence on OCD

Too many candidate genes have been identified

• There has been little success identifying all the genes involved
• Several genes are involved, but each variation increases the risk of OCD by a fraction
• A genetic explanation is unlikely to be very useful, because it provides little predictive value

Environmental risk factors are also invloved

• Environental risk factors can trigger or increase the risk of developing OCD
• Cromer et al (2007): over half the OCD patients they studies experienced a traumatic event
• This supports the diathesis-stress model- focusing on environmental factors can be dealt with more easily than genetics.

Low levels of serotonin

• Neurotransmitters are responsible for relaying information from one neuron to another
• If a person has low levels of serotonin, then normal transission of mood-relevant information doesn't happen, and mood can be lowered because of this

Impairment of frontal lobes

• Some cases of OCD are associated with impaired decision making e.g. hoarding disorder
• This can be associated with abnormal functioning of the lateral frontal lobes in the brain
• The frontal lobes are responsible for logical thinking and decision making

Dysfuncton of the parahippocampal gyrus

• The parahippocampal gyrus is respinsible for processing unpleasant emotions
• There is evidence to suggest this functions abnormally in OCD

Supporting evidence for neural explanations of OCD

• Antidepressants work purely on the serotonin system and reduce OCD symptoms, which suggests the serotonin system is involved in OCD
• OCD symptoms also form part of biological conditions such as Parkinson's disease
• This suggests biological processes that cause the symptomsin those conditions may be responsible for OCD

The serotonin-OCD link may not be unique to OCD

• Many people who suffer from OCD become depressed
• This depression involves the disruption of the serotonin system, which leaves a logical problem when it comes to the erotonin system as  possible basis for OCD
• It could be that the serotonin system is disrupted in many atients with OCD because they are also depressed