Lesson 12 - Biological causes of OCD

Question 1

What are the genetic causes of OCD?

Answer 1

• The COMT gene
• The SERT gene

Question 2

The COMT gene

Answer 2

• a candidate gene for OCD, which is said to be polygenic as many genes can be responsible for OCD behaviour.
• the gene results in high dopamine (high levels of drive, motivation and aggression)
• more common in those with OCD than those without.

Question 3

The SERT gene

Answer 3

Serotonin Transport gene

• results in low serotonin levels, which is associated with low levels of happiness.
• the gene is located on chromosome 17 and a mutation of this can cause OCD.
• Research conducted by Ozaki (2003) found evidence that 6/7 of family members who had OCD had a mutation of the SERT gene. There may be a correlation between this and OCD.

Question 4

Strengths of the genetic explanation of OCD

Answer 4

• Nestadt (2000) supports the genetic explanation as he found that people who had a first degree relative with OCD were five times more likely to also get the illness. This supports the idea that OCD can be transmitted hereditarily
• Billet (1998) supports this as well, as he found from a meta-analysis of 14 twin studies that OCD is twice more likely to be concordant in identical MZ twins rather than DZ twins. Twin studies such as this are useful in ascertaining the extent to which OCD is inherited.

Question 5

Weakness of genetic explanations of OCD

Answer 5

• Concordance rates in twin or family studies into OCD are not 100%, therefore OCD cannot be fully explained with genetics.
• There are alternative explanations such as the behaviourist approach, which would assume that OCD related behaviours may be learnt through Mowrer’s Two Process Model, or traumatic childhood experiences which could trigger OCD, or the interactionist approach which states that genetics and the environment work hand in hand (diathesis stress model).

Question 6

Research study into genetics and OCD by Beekman and Cath

Answer 6

Beekman and Cath (2005)

• Conducted a meta-analysis of twin studies and OCD, DZ twins compared against MZ twins
• 10,034 pairs were studied overall, and they were part of studies where OCD patients had been diagnosed using the DSM criteria
• Results found that in children, OCD inherited via genes ranges form 45-65%
• In adults, it was around 27-47%
• OCD can be transmitted genetically and this was more apparent in children rather than adults.

Question 7

Evaluation of Beekman and Cath’s study

Answer 7

• The methodology can be criticised as the majority of the twin studies used were not performed in controlled conditions. This means that the data is not very objective and scientific and this may affect the validity of the meta-analysis. This brings into question whether OCD is genetic.
• The research can be criticised as it did not consider gene mapping when looking at whether OCD is genetic. Gene mapping would look closely at the DNA of the twins that had OCD and compare this with twins who did not. A comparison needs to be made with a control group of non-OCD sufferers to make this robust.
• It also uses a large sample size, so it had a greater population validity meaning it can be applied to a large group of people and extends the extent to which we can apply the ideas of genetic vulnerability to OCD.

Question 8

The basal ganglia

Answer 8

• responsible for voluntary motor movements, habit learning, eye movements, and over activity could result to repetitive motor functions. Dysfunction can be linked to Tourette’s.
• Hyperactivity in the Caudate Nucleus in the basal ganglia has been linked to repetitive behaviours in OCD.

Question 9

Neurotransmitters

Answer 9

• Low serotonin results in can cause depressive like symptoms
• Low levels can cause the caudate nucleus to malfunction
• High levels of dopamine can be linked to overactivity in the basal ganglia

Question 10

Neuroanatomy by Jenike and Rauch

Answer 10

• Found a relationship between brain damage and OCD
• The brain damage could be caused by a virus
• the damage could effect the short term memory (“I can’t remember if i locked the front door.”) Results in compulsions such as double checking the door
• From PET scans, it shows that when an OCD patient is exposed to something dirty, the frontal lobes and basal ganglia may be overactive.

Supports the idea that the basal ganglia is prominent in finding the cause of OCD.

Question 11

Strengths of the neural explanation of OCD

Answer 11

• There is a lot of research support to back up the idea that neurotransmitters have a role in OCD symptoms. Anti-depressant drugs can increase serotonin levels in OCD and this can lead to a reduction of OCD symptoms. So, this is good evidence that manipulating neurotransmitter levels can either aid or worsen OCD symptoms, but has also given rise to more effective methods of treatment
• Ciccerone (2000) which supports the link between dopamine and OCD through drug therapy
• Menzies (2007) used research support to back up the idea that abnormal brain structure may correlate or cause OCD. This was done through studying MRI scans of OCD patients and healthy controls.
• Rapoport (1990) who found a historic link to OCD in the Great Sleeping Sickness (brain damage/virus)

Question 12

Rapoport (1990)

Answer 12

• supports the neural explanation
• He reviewed the “Great Sleeping Sickness” of 1916-1918, and found a viral brain infections across Europe at the time.
• there was a rise on OCD symptoms as a result
• supports the link between brain damage and OCD

Question 13

Ciccerone (2000)

Answer 13

• when patients were given the drug Risperidone, it resulted in lower dopamine levels and alleviated OCD symptoms

Question 14

Menzies (2007)

Answer 14

Suggested a genetic link to abnormal levels of neurotransmitters.

• He studied MRI scans in OCD patients and immediate family members and compared them with healthy controls. OCD patients and their families had reduced grey matter in key areas of the brain and they had unusual neuroanatomy. This supports Jenike and Rauch’s ideas of dysfunction in the basal ganglia having a role to play in OCD. It also highlights a genetic link as it was present in immediate family members.

Question 15

Weaknesses of neural explanations of OCD

Answer 15

• A disadvantage of the neural explanation is that neurotransmitters may not necessarily cause OCD. On the flip side, it may be a case that OCD instead causes an imbalance of serotonin and dopamine. Therefore cause and effect is unclear despite there being a correlation between the two variables.
• Another problem is that OCD is co-morbid with depression, so it is not clear whether low serotonin levels cause OCD or depression or both.
• The role of dopamine has been questioned. Because high levels of dopamine can also cause other psychological illnesses and not just OCD. For example, high levels of dopamine can cause bipolar depression and schizophrenia. So there is not enough research evidence to suggest that high dopamine levels can cause OCD to occur and it is likely a combination of factors.