Biological Explanations - Genetic Basis Flashcards
What are the biological explanations for schizophrenia?
Genetic basis
Neural correlates
What are genetics?
Genes are inherited and consist of DNA strands. DNA produces ‘instructions’ for general physical features like eye colour of an organism and also specific physical features like neurotransmitter levels.
Genes can also impact on psychological features such as intelligence.
What does the genetic basis of schizophrenia include?
Family studies, candidate genes and mutations.
What is the importance of family studies in schizophrenia?
Family studies have confirmed that risk of schizophrenia increases in line with genetic similarity to a relative with the disorder.
What study supports the importance of family studies in schizophrenia?
Gottesman did a large -scale family study and found that someone with an aunt with schizophrenia has a 2% chance of developing it. It increases to 9% if the individual has a sibling with it and 48% if they are monozygotic twins.
Why are family studies useful in explaining schizophrenia?
Family members tend to share aspects of their environment as well as their genes, so the correlation explains both.
What is the importance of candidate genes in explaining schizophrenia?
Early research into schizophrenia looked for a single genetic variation where one faulty gene explained the condition.
However, it appears that a number of different genes are involved, which makes schizophrenia polygenic.
The genes involved most likely code for neurotransmitters including dopamine.
What study supports the role of candidate genes in explaining schizophrenia?
Ripke et al combined all previous data from genome-wide studies of schizophrenia, which looked at the whole human genome rather than particular genes.
The genetic makeup of 37,000 people with a diagnosis of schizophrenia was compared to that of 113,000 controls. They found 108 separate genetic variations which were associated with slightly increased risk of schizophrenia.
This makes schizophrenia aetiologically heterogeneous, which means that different combinations of factors can lead to the condition (including genetic variation)
What is the role of mutation in the explanation of schizophrenia ?
Schizophrenia can also be due to mutation. This means it has a genetic origin in the absence of family history of the disorder. This could be due to mutation in parental DNA caused by radiation, poison or viral infection.
What is a study that supports the role of mutation in explaining schizophrenia?
Brown et al found that there are positive correlations between parental age and the risk of schizophrenia. This is because as age increases there is an increased risk of sperm mutation.
It increases from around 0.7% with fathers under 25 to over 2% in fathers over 50
What is a strength of the genetic explanation of schizophrenia?
P - One strength is that the genetic explanation has a strong evidence base.
E - Family studies such as that of Gottesman show that risk increases with genetic similarity to a family member with schizophrenia.
Adoption studies such as Tienari et al show that biological children of parents with schizophrenia are at heightened risk even if they grow up in an adoptive family.
E - A recent twin study by Hilker et al showed a concordance rate of 33% for identical twins and 7% for non-identical twins.
L - This shows that some people are more vulnerable to schizophrenia as a result of their genetic makeup.
What is another strength for the genetic explanation of schizophrenia?
P - Another strength of the genetic explanation is that it can allow for genetic counselling.
E - This is because if one or more potential parent have a relative with schizophrenia they risk having a child who would go on to develop schizophrenia. Genetic counselling would allow for parents to reduce the likelihood of having a child who is vulnerable to the disorder.
E - However the risk estimate provided by genetic counselling is just an average figure. This means it will not really reflect the probability of a particular child going on to develop schizophrenia because they will experience a particular environment which also has risk factors.
L - Therefore, genetic counselling can be useful but is is not necessarily accurate.
What is a limitation to the genetic explanation of schizophrenia?
P - One limitation of the genetic explanation is there is clear evidence to show that environmental factors also increase the risk of developing schizophrenia.
E - These include both biological and psychological influences. According to Morgan et al, biological risks include birth complications and Di Forti et al say that smoking THC rich cannabis in teenage years is a biological risk.
Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems in general, but there is now evidence for a particular link with schizophrenia.
E - Recently, Morkved et al found that 67% of people with schizophrenia and related psychotic disorders reported at least one childhood trauma as opposed to 38% of a matched group with non-psychotic mental health issues.
L - This means that genetic factors alone cannot provide a complete explanation for schizophrenia.
