Lesson 2 - Biological explanations of SZ

Question 1

Family studies

Answer 1

Gottesman (1991) found that:

  If **both parents** had SZ – 46% chance of offspring having SZ

  If **one parent** had SZ – 13%

  If a sibling had SZ – 9% 

Shows that the closer you are genetically, the more likely you are to have schizophrenia

Question 2

Twin studies

Answer 2

Gottesman (1991) found that there was a 48% concordance rate between MZ twins and a 17% concordance rate between DZ twins

Supported by more recent evidence – Joseph (2004) did a review of twin studies carried out up to 2001, and found an overall concordance rate for MZ twins as 40% but DZ twins as 7.4%

This shows that the more genetically similar you are then the more likely you are to get SZ

Question 3

Adoption studies

Answer 3

Adoption studies are useful in seeing how nature and nurture influence schizophrenia.

Tienari et al (2001) carried out a study in Finland

• 164 adoptees who’s biological mothers had SZ

  11 (6.7%) were also diagnosed with SZ compared to a control group of 197 adoptees where only 4 (2%) had SZ. 

This shows that although the % of children who also had SZ was low (6.7%) there is a link between genes and SZ

Question 4

Candidate genes

Answer 4

Genes that may be implicated in the development of a condition. SZ is known to be polygenic. Many studies believe that there is a locus of susceptibility on chromosome 8p21-22

Question 5

Gurling et al (2006)

Answer 5

Used gene mapping. Found that the PCM1 gene was implicated in vulnerability to SZ, providing evidence of a genetic basis for SZ.

Question 6

Benzel et al (2007)

Answer 6

Used gene mapping to find evidence suggesting that NRG3 gene variants interact with both NRG1 and ERBB4 gene variants to create susceptibility to developing SZ, suggesting an interaction of genetic factors, supporting the idea that Sz is polygenic

Question 7

Ripke et al (2014)

Answer 7

Compared to genetic makeup of 37,000 SZ patients with 113,000 controls, worldwide. Found 108 operate genetic variations were associated with an increased risk of SZ. The genes that were particularly vulnerable were the ones that had a connection to neurotransmitters like dopamine

Question 8

Strengths of the genetic explanation for SZ

Answer 8

• Wealth of research evidence (Gottesman 1991, Joseph 2004, Tienari 2001) which supports the link between inheritance and SZ. It highlights the fact that even if one parent has SZ, the child may be vulnerable and precautions could be made

Question 9

Weaknesses of the genetic explanation for SZ

Answer 9

• Twin studies may not always provide a good comparison, and it is sometimes difficult to separate nature and nurture. For example, twins raised by the same parent go to the same schools, wear the same clothes and spend lots of time with each other. Upbringing (nurture) may be more impactful that genes. As well as this, adopted children may still be raised in a similar way to their birth parents.
• Age has an impact on SZ, and it can take place in the absence of family history. There may have been a mutation in paternal DNA in sperm cells, which could cause SZ. Brown et al (2002) found that there was a positive correlation between paternal age and increased risk of SZ:

  Under 25 - 0.7%
  Over 50 - 2%

This shows that although no direct genes are involved, offspring can still get SZ if their fathers were old at fertilisation

• Biologically reductionist and determinist. Ignores the role of psychological factors and family upbringing
• The diathesis stress model states that there is a genetic vulnerability but it will only be triggered through a stress trigger. You can be born with a gene that makes you vulnerable, but if you live a stress-free life, you may not end up having the disorder