The Genetic Basis Flashcards
Family studies have confirmed that…
Risk of schiz increases in line with genetic similarity to a relative with the disorder.
- Gottesman’s (1991) large-scale family study.
Family members tend to share aspects of their environment…
As well as many of their genes, so the correlation represents both - but family studies still give good support for the importance of genes in schizophrenia.
Candidate genes.
A single genetic variation in the belief that one faulty gene could explain schizophrenia.
Polygenic.
Number of different genes are involved and the most likely genes would be those coding for neurotransmitters, including dopamine.
Stephen Ripke et al (2014).
Combined all previous data from genome-wide studies of schizophrenia.
The genetic make-up of 37000 ppl with a diagnosis of schiz was compared to that of 113000 controls, 108 separate genetic variations were associated with slightly increased risk of schiz.
Diff studies have identified different candidate genes it also appears that schiz is aetiologically heterogeneous. can leas to the condition.
The role of mutation.
A genetic origin in the absence of a family history of the disorder due to mutation in parental DNA, which can be caused by radiation, poison or viral infection,.
Evidence for mutation comes from positive correlations between paternal age (linked with increased risk of sperm mutation) and risk of schiz, increasing from around 0.7% with fathers under 25 to over 2% in fathres over 50 - Brown et al 2002.
Strength - There is a strong evidence base on the genetic explanation.
Family studies such as Gottesman show that risk increases with genetic similarity to a family member with schiz.
Adoption studies such as Tienari et al (2004) show that biological children of parents with schiz are at heightened risk even if they grow up in an adoptive family.
A recent twin study by Hilker et al (2018) showed a concordance rate of 33% for identical twins and 7% for non-identical twins.
This shows that some ppl are more vulnerable to schiz as a result of their genetic make-up.
Limitation - There is a clear evidence to show that environmental factors also increase the risk of developing schizophrenia.
These environmental factors include both biological and psychological influences.
Biological risk factors include birth complications (Morgan et al 2017) and smoking THC-rich cannabis in teenage yrs (Di Forti et al 2015).
Psychological risk factors include childhood trauma which leaves ppl more vulnerable to adult mental health problems in general but there’s now evidence for a particular link with schiz.
In one study by Morkved et al (2017), 675 of ppl with schiz and related psychotic disorders reported at least one childhood trauma as opposed to 38% of a matched group with non-psychotic mental health issues.
This means that genetic factors alone cannot provide a complete explanation for schiz.
Limitation - A problem with the genetic argument is that it is difficult to separate the impact of nature and nurture.
For example, both family and twin studies investigate individuals who are sharing the same environment, which could be increasing the concordance rates, irrespective of the genes. Possibly the high concordance rates between MZ twins is actually due to them being treated more similarly than DZ twins or ordinary siblings and not in fact due to their genetics. Even MZ twins that are reared apart share the same womb environment before birth. The shared environment could be a confounding variable as we can’t differentiate between genetic and environmental influences.
