genetic exp of Sz

Question 1

how many genes have been found to be associated with sz

Answer 1

more than 100

Question 2

examples of genes linked to excess D2 activity

Answer 2

DRD4, COMT
these could give rise to the hallucinations, delusions and thought disorder associated with the positive symptoms of sz.

Question 3

what is the C4 gene?

Answer 3

• sekar et al identified the gene called complement component 4 on chromosome 6, which is important in the immune system.

Question 4

what is the normal role of C4?

Answer 4

• the brain normally undergoes synaptic pruning during adolescence. this is normally a good thing because it is a part of learning. the brain prunes under used or damaged connections to make space for new ones.

Question 5

how could C4 give rise to symptoms

Answer 5

• the gene plays a role in pruning synapses but excessive synaptic pruning could lead to the symptoms seen.
• this would explain why symptoms appear after adolescence and why the brains of people with it have a thinner cerebral cortex with fewer synapses than healthy brains.
• the genetic explanation is a genuine explanation about the cause of sz and is tied in with our understanding of how evolution works. increased C4 activity has survival value but too much of it backfires.

Question 6

genetic explanations are based on the idea that a disorder has been inherited. there are several ways that genes can be studied.

Answer 6

• specific gene:
  Benzel 2007 found that the three genes COMT, DRD4, AKT2 have all been associated with excess dopamine in specific D2 receptors, leading to acute episodes, positive symptoms.
• family studies:
  kendler has shown that 1st degree relatives of those with sz are 18 times more at risk.
  gotesman and shield 1966 found it was more common in the bio relatives of sz, the closer the degree of genetic relatedness, the greater the risk.
• twin studies:
  concordance for sz is 4 times as high in MZ than DZ. gotesman and shields
• adoption studies:
  Heston 1966 found 10% of the adopted children of schizophrenic mothers grew up to develop sz.

Question 7

application

Answer 7

• identification of genes linked to sz means that ‘at risk’ individuals can be identified by genetic markers.
• a better understanding of the cause of sz may lead to new, better treatments.

Question 8

S/W

Answer 8

:( reductionist to assume that only genetics are related to sz. diathesis stress suggests that environmental factors play a role.
:( labelling family members could be seen as socially sensitive.
:( deterministic because it suggests that sz is inevitable in people with the ‘wrong genes’.
however, by reducing risk factors, we may be able to reduce the chance of developing sz. furthermore, interventions to reduce ‘expressed emotion’ have been found to improve prognosis, suggesting the course of sz is not inevitable.

Question 9

alternative

Answer 9

since there is not a 100% concordance rate for sz in MZ twins, there must be an environmental component. an alternative to a purely genetic explanation is rosenthals diathesis stress model. this proposes that genes may give a person a predisposition, but the full symptoms will not emerge unless they are triggered by environmental stressors.