The Biological Approach to Explaining OCD Flashcards
What are two genes identified which may contribute to OCD
The COMT gene and the SERT gene (5-HTT)
Explain how the COMT gene may contribute to OCD
COMT regulates the production of dopamine, and one allele has been found to be more common in those with OCD than the general population. This variation produces lower activity of the COMT gene and higher levels of dopamine.
Explain how the SERT (5-HTT) gene may contribute to OCD
SERT (5-HTT) affects the transportation of serotonin, creating lower levels of serotonin. These lower levels of serotonin are also implicated in OCD, and a study by Ozaki et al found a mutation of the gene in two unrelated families where 6 of the 7 family members had OCD.
Why is it unlikely there is a simple link between singular genes, like the SERT and COMT gene, and a complex disorder like OCD
Genes like SERT are also implicated in other disorders like depression and PTSD, which suggests that each individual gene only creates a vulnerability for OCD as well as other conditions like depression, and that other stressors affect what condition develops or even if a mental illness develops. This is why people may have a COMT or SERT gene and suffer no effects
What levels of neurotransimitters effect OCD
High Dopamine
Low Serotonin
How is high dopamine associated with OCD
Szechtman et al found that enhanced levels of dopamine induced stereotyped movements resembling compulsive behaviours of OCD in rats.
How is low serotonin associated with OCD
Pigott et al found that antidepressant drugs which increase serotonin activity have been shown to reduce OCD symptoms. In contrast antidepressants which have less effect on serotonin do not reduce OCD symtopms according to Jenicke
Explain the worry circuit
The Orbitofrontal cortex sends signals to the thalamus about things which are worrying, like a potetial hazard, and from the thalamus signals are sent around the body. The Caudate Nucleus normally supresses signals from the OFC, but if it is damaged than it fails to suppress minor ‘worry’ signals and the thalamus is alerted
How have PET scans supported the caudate nucleus
PET scans of patients with OCD, taken while symptoms are active, have shown increased activity in the Orbitofrontal cortex
How are dopamine and serotonin linked to the worry circuit
Comer reports that serotonin plays a key role in the operation of the Orbitofrontal cortex and caudate nuclei, and so low levels of serotonin could cause these areas to malfunction
Dopamine is the main nerotransmitter in the basal ganglia, and high levels of dopamine lead to overactivity in this region
Who found that low serotonin may cause malfunction in the worry circuit
Comer
Who found that antidepressants help with OCD
Pigott
Who found that rats with too much dopamine went a little OCD on us
Szechtman
Who found the SERT gene in plenty of two seperate families with 6/7 members of family having OCD
Ozaki
How have first-degree relative studies supported a genetic basis for OCD
Nestadt et al identified 80 patients with OCD and 343 of their first degree relatives, comparing them to 73 control patients without mental illness and 300 of their relatives. They found people with a first-degree relative with OCD had a 5x greater risk of having the illness themselves versus the general population.
How have twin studies supported a genetic basis for OCD
Billett et al conducted a meta-analysis of 14 twin studies of OCD, and found that on average, monozygotic twins were more than twice as likely to develop OCD if their co-twin had the disorder than was the case for dizygotic twins. However concordance rates are never 100% meaning other factors must also be present
Who conducted a meta analysis of 14 twin studies into OCD
Billett et al
Who conducted first-degree relative studies into those with OCD
Nestadt et al
How have studies into different disorders supported the biological basis of OCD
Pauls and Leckman studied patients with Tourette’s syndrome and their families, and concluded that OCD was just one expression of the same gene which causes Tourette’s syndrome. Obsessive behavior in OCD is also present in autistic children and those with anorexia. All these comorbid symptoms suggest there is no specific OCD gene, but genes act as a predisposing factor for obsessive behaviour
Who studied people with tourettes syndrome and concluded that OCD was an expression of the same gene as tourettes
Pauls and Leckman
What real life applications does the biologial approach to OCD have
Mapping of the human genome has led to hope that specific genes can be linked to certain disorders. For example, where one parent has the COMT gene a baby from this parent can be screened and parents can have the choice to abort the child if they have the gene. Alternatively gene therapy may be able to turn genes ‘off’ so that the disorder is never expressed.
What issues do real life applications of the biological approach to OCD raise
There are many ethical issues with aborting OCD children, and the gene screeing relies on a simple relationship betweem genes and the disorder, which we have already evaluated there is not
What is an alternative explination to OCD (other than the biological approach)
The two-process model can be applied to OCD, similar to the behaviourist approach to phobias. Initial learning occurs resulting in anxiety and the association is maintained as the anxiety provoking stimulus is avoided. The obsession is formed as people learn that compulsive behaviours seem to alleviate anxiety.
What supports the two-process model of OCD
The successful treatment of patients using exposure and response prevention (ERP), which is similar to systematic desensitisation. Patients are exposed to the fear stimulus and at the same time prevented from performing compulsive behaviours. Albucher reprted between 60% and 90% of adults with OCD had improved considerably using ERP.
Who reported successful results from Exposure and Response Prevention therapy
Albucher reported 60% - 90% of adults with OCD improved considerably
