Biological approach- explaining OCD

• Some mental disorders appear to have a stronger biological component than others, OCD is a good example of a condition that may be largely understood as biological in nature.
• Genes are involved in individual vulnerability to OCD. In a classic study, Lewis observed that of his OCD patients, 37% had parents with OCD and 21% had siblings with OCD. This suggests OCD runs in families, although what is probably passed on is the genetic vulnerability not the certainty of OCD.
• According to the diathesis-stress model certain genes leave some people more likely to develop a mental disorder but it is not certain. Some environmental stress is necessary to trigger the condition.
• Researchers have identified genes which create vulnerability for OCD called candidate genes. Some of these genes are involved in regulating the development of the serotonin system.
• However, OCD seems to be polygenic. This means that OCD is not caused by one single gene but by a combination of genetic variations that together significantly increase vulnerability.
• Taylor has analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD. Genes that have been studied in relation to OCD include those associated with the action of dopamine as well as serotonin, both neurotransmitters believed to have a role in regulating mood.
• One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person. The term used to describe this is aetiologically heterogenous, meaning that the origins of OCD vary from one person to another.
• There is also some evidence to suggest that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession.
• The genes associated with OCD are likely to affect the levels of key neurotransmitters as well as structures of the brain. These are neural explanations.
• One explanation of OCD concerns the role of the neurotransmitter serotonin, which is believed to help regulate mood. Neurotransmitters are responsible for relaying information from one neuron to another. If a person had low levels of serotonin then normal transmission of mood-relevant information does not take place and a person may experience low moods. At least some cases of OCD may be explained by a reduction in the functioning of the serotonin system in the brain.
• Some cases of OCD seem to be associated with impaired decision-making. This in turn may be associated with abnormal functioning of the lateral of the frontal lobes. The frontal lobes are responsible for logical thinking and making decisions. There is also evidence to suggest that an area called the left parahippocampal gyrus, associated with processing unpleasant emotions, functions abnormally in OCD.
• A strength if the genetic explanation for OCD is the evidence from a variety of sources which strongly suggest that some people are vulnerable to OCD as a result of their genetic make-up. Nestadt et al. reviewed twin studies and found that 68% of identical twins shared OCD as opposed to 31% of non-identical twins. Research has also found that a person with a family member diagnosed with OCD is around four times as likely to develop it as someone without. This suggests there must be some genetic influence on the development of OCD.
• A limitation of the genetic model of OCD is that there are also environmental risk factors. OCD does not appear entirely genetic in origin and it seems that environmental risk factors can also trigger or increase the risk of developing OCD. For example, Cromer et al. found that over half the OCD clients in their sample had experienced a traumatic event in their past. OCD was also more sever in those with one or more traumas. This means genetic vulnerability only provides a partial explanation for OCD.
• A strength of the neural model of OCD is the existence of some supporting evidence. Antidepressants that work purely on serotonin are effective in reducing OCD symptoms and this suggests that serotonin may be involved in OCD. Also, OCD symptoms form part of conditions that are known to be biological in origin, such as the degenerative brain disorder Parkinson’s disease, which causes muscle tremors and paralysis. If a biological disorder produces OCD symptoms, then we may assume the biological processes underlie OCD.
• One limitation of the neural model is that the serotonin-OCD link may not be unique to OCD. Many people with OCD also experience clinical depression. Having two disorders together is called co-morbidity. This depression probably involves disruption to the action of serotonin. This leaves us with a logical problem when it comes to serotonin as a possible basis for OCD. It could simply be that serotonin activity is disrupted in many people with OCD because they are depressed as well. This means serotonin may not be relevant to OCD symptoms.