Genetics explaining Sz

Question 1

What are the 3 biological causes of Schizophrenia that involve genetics?

Answer 1

C4 Gene
22qDS Deletion Syndrome
COMT gene

Question 2

How does the C4 Gene explain Sz? (4 points)

Answer 2

Synaptic pruning occurs during adolescence - excess synaptic connections are removed to prepare for new neuronal connections

C4 plays a role in pruning synapses - excessive pruning can lead to the symptoms of Sz

Test mice with increased levels of C4 activity lost more brain cells as they matured

Explains why Sz symptoms appear during adolescence and why Sz brains have a lower volume and thinner cerebral cortex

Question 3

How does 22qDS Deletion Syndrome explain Sz? (4 points)

Answer 3

It is a gene mutation which results in the phenotypic expression of SZ

Approximately 1% of patients with Sz have 22qDS

Those with it have lower IQs than those with other forms of Sz

The syndrome causes changes in brain anatomy and neuropathology which causes physical and cognitive deficit symptoms

Question 4

How does the COMT gene explain Sz? (3 points)

Answer 4

Cathechol-O-Methyl Transferase (COMT) - an enzyme which normally catalyses the breakdown of dopamine

A mutation in the COMT gene can cause regulation of dopamine breakdown to malfunction - resulting in positive and negative symptoms of Sz

Located on chromosome 22 - deletion to this region makes people 30 times more likely to develop Sz

Question 5

What are the 3 supporting and 2 refuting pieces of evidence for genetics as an explanation of Sz?

Answer 5

Supporting:
Heston (1996)
Gottesman & Shields (1966)
Inouye (1961)

Refuting:
Diathesis-stress model
Tiwari et al (2010)

Question 6

How does Heston (1996) support genetics as an explanation of Sz? (4 points)

Answer 6

Investigated whether Sz has a genetic predisposition and to study the nature V nurture debate

Took place at Oregon State psychiatric hospital US using 58 participants born in 1915-1945

IV: Adopted participants with/without a schizophrenic biological mother

Results showed Sz diagnosis for adopted participants with a Sz biological mother was 10.6% compared with 0% in control group

Question 7

How does Gottesman & Shields (1966) support genetics as an explanation for Sz? (3 points)

Answer 7

Investigated agenetic basisfor schizophrenia and compared the concordance rates of Sz between MZ and DZ twins

Results showed a higher concordance rate for schizophrenia in MZ twins (75%) than DZ twins (22%)

Question 8

How does Inouye (1961) support genetics as an explanation for Sz? (2 points)

Answer 8

Cross cultural research in Japan supports the findings of Gottesman & Shields

74% concordance rate of progressive chronic Sz in MZ twins.

Question 9

How does the diathesis-stress model challenge genetics as an explanation of Sz? (2 points)

Answer 9

Gottesman & Shields (1966) found MZ twins concordance was 75%, not 100% - suggests that Sz is not caused entirely by genes and environmental factors must play a role

Diathesis-stress model - explains a disorder as the result of an interaction between a pre-dispositional vulnerability and stress caused by life experiences

Question 10

How does Tiwari et al (2010) challenges genetics as an explanation of Sz? (3 points)

Answer 10

Found out that less than 1/3 of people with Sz have a family history, suggesting a more complex role of genes

Because 2/3 of Sz cases are sporadic, it is unlikely that it is caused by a mutation like the deletion of 22q11

Copy variants (mutations) are also submicroscopic - difficult to study