Biological explanations; Genetics

Question 1

Genetics and schizophrenia

Answer 1

• Not a single gene; many genes involved
• Not the sole cause; genes only increase risk
• Liability threshold model; more genes, more risk, some risker than others
• Diathesis stress model; genes put one at risk, stressors trigger illness

Question 2

Biological explanation of schizophrenia

Answer 2

• We inherit 50% of our genes from each parent
• Genes build bodies including brains
• the arrangement of DNA elements on a gene becomes the building block of a protein or enzyme; these build cells that form the body. So genes are like chemical ‘codes’ for the construction of every human cell.
• The brain is the source of all mental states
• Schizophrenia is a disorder of mental states

Question 3

If genes determine our brain structure…

Answer 3

Then these determine our thoughts and behaviours and so schizophrenia may be heritable

Question 4

Diathesis stress model

Answer 4

-The genes are the diathesis, as they put someone at risk and the stressors are the environmental factors that determine who develops the disorder and when.

Question 5

Liability threshold model

Answer 5

The more of these genes you have the higher your risk is of schizophrenia

Question 6

Combining the models

Answer 6

• The higher your LT is, they will be more at risk and require minor environmental effects to trigger it
• Those with a lower LT, will require a more serious stressor to develop the illness

Question 7

Twin study: Gottesman review

Answer 7

• Reviewed results from about 40 twin studies and pooled the results, which essentially makes this a meta-analysis
• The pooled concordance rate for MZ twins reared together was 48% and for DZ twins reared together it was 17%
• The concordance rate for MZ twins reared apart was 58%, although is was on the basis of only 14 pairs of twins.

Question 8

Adoption studies: Tienari (1987) + (2000)

Answer 8

(1987)
-Finnish adopted children who had schizophrenic mothers had a 7% chance of developing schizophrenia compared to 1.5% of the controls (who were also adopted children with non-schizophrenic mothers)
(2000)
-The risk for developing schizophrenia was 4 times greater in adopted children with schizophrenic biological mother compared to adopted children from biological mothers with schizophrenia.

Question 9

Adopted studies: Wahlberg et al. (2000)

Answer 9

-He re-examined the Tienari et al data (20000) and found a strong effect of environmental factors where those at risk of developing schizophrenia were adopted into families with poor communication.

Question 10

Molecular genetics: Allen et al (2008)

Answer 10

• 118 Meta-analyses, 24 genetic variants in 16 different genes showed nominally significant effects with average summary odds ratio of approximately 1.23, an increase in risk of 23%
• 4 of the top 10 gene variants most strongly associated with schizophrenia are directly involved in dopaminergic pathways.

Question 11

Methodological issues: Twin studies

Answer 11

-MZ’s may be treated more similarly than DZ’s because they look more alike. This could mean that MZ’s are more similar in concordance rates for schizophrenia for environmental reasons rather than for genetic reasons, which is the underlying assumption of the twin study method.

Question 12

Methodological issues: Adoption studies

Answer 12

• Adoptive parents were likely to be aware of mental illness in genetic parents because the information is available.
• Adoptees with a mother with S are more likely to be placed in more ‘psychologically harmful’ adoptive homes, because better informed adoptive parents would not have chosen a child with a mentally ill parent.
• This could account for the higher rates of S than in control cases; the children with mothers with schizophrenia were more likely to be placed in homes which were environmentally stressful, and thus more likely to develop schizophrenia.

Question 13

Example PEE (point, evidence, explain): Evaluating theories

Answer 13

P- If genes play a role in schizophrenia then we would expect the concordance rate for adopted children to be high
E- Tienari et al. found that adopted children who had a schizophrenic mother had a 7% chance of developing schizophrenia compared to 1.5% of the controls.
E- This provides moderate evidence for the role of genetics because although the percentages are not very high, the percentage of those with schizophrenic mothers is four times the percentage to those without and so the fact that they have it is likely to be due to genetics and less likely to be environmental.

Question 14

Example PEE (point, elaborate, explain): Evaluating methodological evidence

Answer 14

P- A problem in adoption studies is that selective placement might occur
E- It could occur that adopted children with a schizophrenic mother are more likely to be adopted into a more psychologically harmful home as the adoptee parents who are informed of their illness would not have chosen a child with a history of schizophrenia
E- This then could suggest that their are higher rates in control cases as the children with a schizophrenic mother would be placed in a harmful home and therefore would be more likely to develop schizophrenia. This is a problem in studies because it shows that the adopted children may be at a higher risk anyway.