The Biological Explanation for Schizophrenia Flashcards
Genetic Basis for Schizophrenia
- You are more likely to have schizophrenia if someone in your family has schizophrenia.
- Indeed, how related you are to someone with schizophrenia correlates with how likely you are to have schizophrenia.
Gottesman and Shields (1972) ‘A review of recent adoption twin and family studies of Schizophrenia’
- In total there were 711 participants in the adoption studies. In the twin studies a total of 210 monozygotic twin pairs and 319 dizygotic twin pairs were studied. It reviewed 7 different studies.
- Adopted children with biological parents who are schizophrenic have high rate of schizophrenia.
- Fostered child with schizophrenic foster parents do not show high prevalence of schizophrenia.
- Adopted child to an adoptive parent with schizophrenic children do not show high prevalence of schizophrenia.
- In childhood, having an adoptive sibling with schizophrenia gives you a 6.3% chance of having schizophrenia – this is higher but not significantly.
Early adulthood
Many genes identified, indicating synapse development, plasticity, converging mechanisms.
Large number of synapses are permanently removed over time by pruning.
Critical periods for pruning is different for different parts of the brain.
Schiz could be caused by too much pruning.
Largest risk in chromosome 6 – gene is c4 (immune related gene)
Excessive pruning is caused by the gene tagging too many synapse.
Ripke et al. (2014)
- Alleles of C4 are associated with schizophrenia, with high expression of C4A causing greater risk to the disorder.
- C4A is associated with the immune system.
- However, one of these immune functions may be going awry, with it destroying synaptic connections in the brain. This is done in all people (pruning) but in schizophrenia, the excess of C4A leads to too much pruning.
- C4 is dopaminergic.
Investigated by Gottesman et al.
This makes sense as the more related you are to someone, the more genes you share. In monozygotic twins, 100% of your genes are identical. Whereas if you are dizygotic, then this drops to 50%.
- Consequently, if there were a hereditable component to schizophrenia, you would expect that those who are more related, the greater the chance of them sharing the disorder.
- Gottesman shows that there must be a genetic component, as the more related you are to someone with schizophrenia, the more likely you are to have schizophrenia.
Original dopamine hypothesis
High levels/activity of dopamine (hyperdopaminergia) in subcortical brain areas.
Updated version
Abnormally low dopamine levels/activity (hypodopaminergia) in brain’s cortex leads to hyperdopaminergia in subcortical areas.
eval understanding strength
One application of our understanding of the likely role of genes in schizophrenia is genetic counselling. If one or more potential parents have a relative with schizophrenia, they risk having a child who would go on to develop the condition. For example, based on Gottesman’s study they will have a 2% probability if they have an uncle or aunt with schizophrenia, and a 6% probability if they have a half-sibling with it. Genetic counselling involves informing potential parents of these probabilities so that they can make informed choices about whether to have children who risk having a poor quality of life if they develop schizophrenia.
eval understanding weakness
However, the risk estimate provided by genetic counselling is just an average figure based on risk across the whole population. It will not really reflect the probability of a particular child going on to develop schizophrenia because any given child will experience a particular environment which also exposes the child to risk factors. For example, a child’s risk of going on to develop schizophrenia will be much higher than is suggested by their genetic probability if they go on to experience a childhood trauma and then smoke cannabis in their teens. However their risk will be less than the average if they do not experience these environmental risks because the average includes those who do experience them.
This means that genetic counselling only provides a crude estimate of the risk of an unborn child going on to develop schizophrenia.
eval understanding conclusioon
This means that genetic counselling only provides a crude estimate of the risk of an unborn child going on to develop schizophrenia.
the role of mutation
schixophernia can also have a genetic orgiun in the absence of a family history of the disorder
one explanation for this is mutation in parental DNA which can be caused by radiation poison or viral infection
evidence for mutation comes from positive correlation between paternal age and risk of schopherina increasing from around 0.7% with fathers under 25 to over 2% in fathers over 50
brown et al
candidate genes
early research in this area looked for a single genetic variation in the belief that one faulty gene could explain schipherina
however it appears that a number of different genes are involved could be polygenic
the most likely genes would be those coding for neurtoansmitters including dopamine
one strength research support
Gottesman shows that there must be a genetic component, as the more related you are to someone with schizophrenia, the more likely you are to have schizophrenia.
Riki hiller shows a coordance rate of 33% for identical 7% for non identical
Tenari shows that biological offspring of parents withschrizopheria are at risk even if they are raised in an adoptive family
