Biological explanations for schizophrenia Flashcards
what does genetic basis of schizophrenia include
family studies
candidate genes
the role of mutation
genetic basis of schizophrenia - family studies
Family studies have confirmed the risk of schizophrenia increases in line with genetic similarity to a relative with the disorder. For example, someone with an aunt with schizophrenia has a 2% chance of developing it, increasing to 9% if the individual is a sibling and 48% if they are an identical twin.
genetic basis of schizophrenia - candidate genes
Early research believed one faulty gene could explain schizophrenia. However, it appears a number of genes are involved meaning schizophrenia is polygenic. The most likely genes would be those coding for neurotransmitters including dopamine. Ripke et al (2014) combined all previous data from genome-wide studies of schizophrenia. The genetic make-up of 37,000 people with schizophrenia were compared to 113,000 controls. 108 separate genetic variations were associated with slightly increased risk of schizophrenia. Because different studies have identified different candidate genes it also appears that schizophrenia is aetiologically heterogenous.
genetic basis of schizophrenia - the role of mutation
Schizophrenia can have a genetic origin in the absence of a family history of the disorder. One explanation is the mutation of parental DNA which can be caused by radiation, poison or viral infection. Evidence for mutation comes from positive correlations between paternal age and risk of schizophrenia. Increasing from around 0.7% with fathers under 25 to over 2% in fathers over 50.
Evaluation of genetic basis of schizophrenia (brief)
:) research support from adoption and twin studies
:( environmental factors also increase risk of SZ
strength of genetic basis of schizophrenia
there is strong research support for genetic basis. Family studies such as Gottesman show that risk increases with genetic similarity to a family member with schizophrenia. Adoption studies such as Tienari et al (2004) show that biological children of parents with schizophrenia are at a 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 people are more vulnerable to schizophrenia due to their genetic make-up.
weakness of genetic basis of schizophrenia
there is clear evidence 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 and smoking THC-rich cannabis in teenage years. Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems particularly schizophrenia. Morkved et al (2017) found 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. This means that genetic factors alone cannot provide a complete explanation of schizophrenia.
what does neural correlates of schizophrenia include
dopamine hypothesis
neural correlates
neural correlates of schizophrenia - dopamine hypothesis
Dopamine is a neurotransmitter that usually has an excitatory effect and linked to the sensation of pleasure.
Dopamine hypothesis suggests an overactivity of dopamine (hyperdopaminergia) in the subcortex contributes to positive symptoms e.g. hallucinations. While an underactivity of dopamine (hypodopaminergia) in the prefrontal cortex contributes to negative symptoms e.g. avolition.
neural correlates of schizophrenia - neural correlates
the ventral striatum is associated with motivation and goal directed behaviour and reduced activity in this region is linked to avolition. All et al (2006) and Juckel et al (2006) provided research supporting the link between reduced ventral striatum activity and negative symptoms in schizophrenia.
Evaluation of neural correlates (brief)
:) evidence dopamine is involved in SZ
:( evidence for role of glutamate
strength of neural correlates of schizophrenia
there is evidence that dopamine is involved in schizophrenia. First, amphetamines increases dopamine and worsen symptoms in people with schizophrenia and induce symptoms in people without. Second, antipsychotic drugs reduce dopamine activity and also reduce the intensity of symptoms. Third, some candidate genes act on the production of dopamine and dopamine receptors.Therefore, this suggests that dopamine plays a role in schizophrenia.
weakness of neural correlates of schizophrenia
a limitation of the dopamine hypothesis is evidence for a central role of glutamate. Post-mortem and live scanning studies have consistently found raised levels of the neurotransmitters glutamate in several brain regions of people with schizophrenia. In addition, several candidate genes for schizophrenia are believed to be involved in glutamate production or processing. This means that other neurotransmitters other than dopamine may be the true cause of symptoms in schizophrenia.
