Genetic explanation for Sz Flashcards
What does the genetic explanation for Sz suggest?
Sz is heritable –> inherited through generations through transmission of genes.
Runs in families
How does family studies study Sz?
Find individuals with Sz
Determine wither biological relatives similarly affected more often than non-relatives
Gottesman (1991):
Found concordance rates of children if:
2 Sz parents = 46%
1 Sz parent = 13%
Sz sibling = 9%
What do twin studies tell us about Sz?
If MZ twins > DZ twins in concordance rates = similarity due to genes
Joseph (2004):
Meta-analysis of twin studies conducted b4 2001 found concordance rate of:
40% for MZ
7% for DZ
What do adoption studies tell us about Sz?
Studies of genetically related individuals who ahve been reared separately
Tienari et al (2000):
164 adoptees with Sz mothers
~~~>11 (6.7%) received diagnosis
197 control adoptees
~~~> 2% received diagnosis
Weakens ‘nurture’ argument.
What does concordance rate mean?
Percentage of pairs of twins/relatives who exhibit a particular trait/disorder.
What impact do candidate genes have on Sz?
Nucifora et al (2012) –> found link between mutations in NPAS3 gene and Sz
How many candidate genes associated with Sz?
Ripke et al (genome wide study)
108 separate candidate genes associated with Sz.
Sz = polygenic
Define candidate genes:
Genes that put you at risk of developing the disorder.
Define polygenic:
Multiple genes that put you at risk
Define aetiologically heterogeneous:
Multiple reasons why disorder occurs
What is the role of mutations in Sz?
Mutation in parental DNA can lead to a family history of SZ
~radiation
~viral infection
~poison
Evidence for mutation:
Brown et al (2002):
Positive correlations between paternal age (increased sperm mutations) + risk of Sz
Increased from 0.7% with fathers under 25 to over 2% to fathers over 50
Evaluation of genetic explanation:
Research support:
Strong evidence basis
Family studies –> Gottesman et al = risk increases with genetic similarity.
Adoption studies –> Tienari –> biological children of Sz patients = higher risk even in adoptive families
Hilker (2018): Concordance rate of:
33% = MZ
7% = DZ
Evaluation of genetic explanation:
Environmental factors:
Clear evidence showing environmental factors increase Sz:
Biological risk factors:
~>Birth complications
(Morgan et al 2017)
~>Smoking THC-rich cannabis in teenage years (Di Forti 2015)
Psychological risk factors:
~>Childhood trauma –> diathesis
Mørkved (2017):
67% Sz patients + related psychotic disorders = at least 1 childhood trauma
38% matched group with no psychotic mental health issues.
Genetic factors = incomplete explanation.
Evaluation for genetic explanation
Genetic counselling:
Practical application
1 or more parent = relative with Sz –> risk of child having disorder.
Informing potential parents of probabilities –> poor quality of life with Sz
HOWEVER –> average figure based on risks across whole population.
Not really reflects probability of particular child –> environmental factors (smoking cannabis in teen life) also prevalent.
Only provides crude estimate of risks.
