Biological explanations for OCD

Question 1

Discuss Genetics

Answer 1

Genetics is the study of genes and inheritance.
OCD seems to be a polygenic condition, where a number of inherited genes are involved in its development.
- Family and twin studies suggest the involvement of genetic factors. The prevalence of OCD in the population is approximately 2–3%.
Two candidate genes: COMT and SERT have been identified:

Question 2

Describe COMT:

Answer 2

• A gene that regulates the function and appropriate levels of dopamine and norepinephrine.
• It is particularly important in the prefrontal cortex, a region is involved with decision making, inhibition of behaviours, abstract thinking and working memory.
• COMT helps maintain appropriate levels of these neurotransmitters in this part of the brain in people without OCD.
• The mutated variation of the COMT gene found in OCD individuals causes a decrease in the COMT activity and therefore a higher level of dopamine.
• Excessive dopamine and norepinephrine in the PFC is
  linked to obsessionality and lacking inhibition for behaviours, as seen in OCD patients.

Question 3

Describe SERT:

Answer 3

• The SERT gene is responsible for the production of serotonin transporters.
• The Sert Gene affects the transportation of serotonin, causing lower levels of the neurotransmitter serotonin, which is associated with OCD
• Recent research suggests that a specific variation plays an important role in the PFC.
• This structure is involved in controlling attention and resisting temptations, both of which are associated with OCD symptoms.
  -Hence, some of the symptoms of OCD may be caused by the effects of SERT on the PFC.

Question 4

A03 - Genetic Evaluation

Answer 4

• Genetic explanations are both supported and challenged by MZ/DZ research.
• Billett et al (1998) conducted a meta-analysis of 14 twin studies of OCD, including 80 identical and 29 fraternal twin pairs, and found that MZ twins were on average more than twice as likely to develop OCD if their twin had the disorder than were DZ twins.
• As MZ and DZ twins have 100% and 50% genetic similarity, genes are likely to significantly influence OCD onset.
• However, if OCD were solely due to genetics, we should expect 100% concordance rates for MZ twins.
• Hence, other factors, such as learning or experiences are also likely to contribute to the onset of OCD.
• This might be explained by the diathesis-stress model that suggests that a person who develops OCD is born with a genetic predisposition (the diathesis) towards developing OCD.
• Hence, these genetic explanations do not provide a comprehensive explanation of the cause of OCD.