OCD (Biological explanations of OCD)

Question 1

The genetic explanation (overview)

Answer 1

• Suggests that vulnerability to OCD is inherited.
• Research has consistently shown that OCD runs in families from one generation to the next.
• The general prevalence rate of OCD is 2%, but the risk of developing this illness is much higher if you share the same genes as someone else who suffers.

Question 2

Twin and family studies

Answer 2

• Provide convincing evidence for the importance of genetic factors in the expression of OCD.

Carey & Gottesman= found a concordance rate of 87% for monozygotic (identical twins) and 47% dizygotic (non-identical) twins.

Question 3

Twin pairs= assumptions made.

Answer 3

• Assuming that twin pairs (both MZ and DZ) share equally similar environments, the consistently higher concordance rates in monozygotic twins lends strong support for a genetic basis for vulnerability to OCD. These very high concordance rates make OCD one of the most heritable illnesses.

Question 4

Polygenic disorder

Answer 4

• Researchers have identified over 230 genes that are linked to OCD and different combinations of these genes have been linked to different types of OCD. This shows that OCD is a polygenic disorder.

Question 5

Neurochemistry & Genes

Answer 5

• Both serotonin and dopamine are neurotransmitters that play important roles in the regulation of moods.
• Research has identified common genes that code for the activity of these neurotransmitters in patients with OCD.

Question 6

COMT gene info

Answer 6

• Codes for an enzyme that breaks down dopamine and clears it away from the receptors in the synapse.
• A ‘low activity allele’ of this gene has been identified in patients with OCD.
• Low levels of this enzyme cause high levels of dopamine activity and the symptoms of OCD.

Question 7

SERT + 5-HTT gene

Answer 7

• They are genes that code for the density of serotonin receptors at the synapse and for the action of serotonin transporter molecules, and they have been linked to vulnerability to OCD.
• One explanation is that serotonin may be removed too quickly from the synapse and that the transmission of the mood- relevant info is not passed on. It has been suggested that low levels of serotonin may also make people hyper-aware of their environments- these effects are thought to increase vulnerability to OCD.

Question 8

Neuroanatomy

Answer 8

• Reduced SERT availability has been identified in OCD patients, in particular, in a neural circuit involving the thalamus and the basal ganglia.

Question 9

What does the neural explanation suggest?

Answer 9

• This neural explanation suggests that there is abnormal functioning in a specific area of the brain known as ‘the worry circuit’.

Question 10

What happens in ‘the worry circuit’?

Answer 10

• Brain imaging studies have shown heightened activity in the orbital frontal cortex, an area of the brain that converts sensory info into thoughts and actions.
• This hyperactivity means that ‘worries’ are repeatedly generated. these thoughts are intrusive and cannot be suppressed, causing high levels of anxiety and distress.

Question 11

Brain structure- ‘faulty filter’

Answer 11

• Irrelevant thoughts and minor worries are normally filtered out by the basal ganglia. the brain structure responsible for facilitating wanted behaviours and stopping unwanted behaviours.
• This ‘filter’ is faulty in OCD and worries (that have become obsessions) are passed onto the thalamus which sends signals to the motor cortex, where movements are controlled.
• The thoughts are converted into actions, resulting in compulsive behaviours.
  *Compulsions can be an attempt to reduce anxiety.

Question 12

What is genetic vulnerability?

Answer 12

• The increased likelihood of developing a certain diseased based on one’s genetic makeup.

Question 13

What is meant by a genetic marker?

Answer 13

• The name of a gene or a segment of DNA that has an identifiable location of the chromosome and inheritance is tracked.