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What is a potential reasoning behind the genetic vulnerability for schizophrenia among individuals who have never been diagnosed with the illness themselves?
What is a potential reasoning behind the genetic vulnerability for schizophrenia among individuals who have never been diagnosed with the illness themselves?
Why have twin studies been criticized in the context of schizophrenia research?
Why have twin studies been criticized in the context of schizophrenia research?
What were the reported concordance rates for schizophrenia in MZ and DZ twins in the Danish twin study?
What were the reported concordance rates for schizophrenia in MZ and DZ twins in the Danish twin study?
What flaw does the proband wise method introduce in the concordance rate calculations for twin studies?
What flaw does the proband wise method introduce in the concordance rate calculations for twin studies?
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According to Hilker et al.'s study, what is the estimated genetic heritability of schizophrenia?
According to Hilker et al.'s study, what is the estimated genetic heritability of schizophrenia?
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Which of the following is NOT an assumption made in the modeling process used to calculate genetic heritability in twin studies?
Which of the following is NOT an assumption made in the modeling process used to calculate genetic heritability in twin studies?
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What was the primary outcome measured in the study involving adoptees?
What was the primary outcome measured in the study involving adoptees?
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What criticism is aimed at typical assumptions in twin studies regarding MZ and DZ twins?
What criticism is aimed at typical assumptions in twin studies regarding MZ and DZ twins?
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What is a common misconception about the representation of twins in studies?
What is a common misconception about the representation of twins in studies?
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In the study, how were the two groups of adoptees categorized?
In the study, how were the two groups of adoptees categorized?
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What method was employed to assess the family-rearing environments of the adoptees?
What method was employed to assess the family-rearing environments of the adoptees?
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What was found to increase the probability of schizophrenia in high-genetic-risk children?
What was found to increase the probability of schizophrenia in high-genetic-risk children?
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According to the study's findings, what was a protective factor against developing schizophrenia?
According to the study's findings, what was a protective factor against developing schizophrenia?
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What does the diathesis-stress model imply in the context of the study?
What does the diathesis-stress model imply in the context of the study?
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Which statement reflects the conclusion regarding the genetic basis of schizophrenia in the study?
Which statement reflects the conclusion regarding the genetic basis of schizophrenia in the study?
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What was the main demographic factor matched between the two groups in the study?
What was the main demographic factor matched between the two groups in the study?
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What is the primary finding related to the concordance rates in MZ twins regarding schizophrenia?
What is the primary finding related to the concordance rates in MZ twins regarding schizophrenia?
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Which method was used to support the genetic interpretation of high concordance rates for schizophrenia in twins?
Which method was used to support the genetic interpretation of high concordance rates for schizophrenia in twins?
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What does the data suggest about individuals who carry genes for schizophrenia but do not express the disorder?
What does the data suggest about individuals who carry genes for schizophrenia but do not express the disorder?
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Why is it stated that genetics alone cannot explain schizophrenia fully?
Why is it stated that genetics alone cannot explain schizophrenia fully?
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In the context of schizophrenia, what does the term 'discordant twins' refer to?
In the context of schizophrenia, what does the term 'discordant twins' refer to?
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What was a significant insight provided by Gottesman and Bertelson's study regarding the children of MZ twins?
What was a significant insight provided by Gottesman and Bertelson's study regarding the children of MZ twins?
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Which type of studies are mentioned as supporting evidence for the genetic predisposition of schizophrenia?
Which type of studies are mentioned as supporting evidence for the genetic predisposition of schizophrenia?
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Which of the following is a significant limitation of twin studies in the context of schizophrenia research?
Which of the following is a significant limitation of twin studies in the context of schizophrenia research?
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What do adoption studies primarily aim to do in schizophrenia research?
What do adoption studies primarily aim to do in schizophrenia research?
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According to Kety's research in Denmark, what was observed in the biological relatives of adoptees with schizophrenia?
According to Kety's research in Denmark, what was observed in the biological relatives of adoptees with schizophrenia?
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What was the main hypothesis tested in adoption studies regarding adults with schizophrenia?
What was the main hypothesis tested in adoption studies regarding adults with schizophrenia?
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One reason twin studies can misrepresent genetic heritability estimates is due to what potential issue?
One reason twin studies can misrepresent genetic heritability estimates is due to what potential issue?
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Which finding supports the genetic basis for schizophrenia according to adoption studies?
Which finding supports the genetic basis for schizophrenia according to adoption studies?
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In Tienari et al.’s study, what aspect was significantly examined regarding the development of schizophrenia spectrum disorders?
In Tienari et al.’s study, what aspect was significantly examined regarding the development of schizophrenia spectrum disorders?
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What is a clear advantage of adoption studies compared to twin studies in schizophrenia research?
What is a clear advantage of adoption studies compared to twin studies in schizophrenia research?
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What role does the DISC1 gene play in brain development?
What role does the DISC1 gene play in brain development?
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Which gene is associated with metabolizing dopamine?
Which gene is associated with metabolizing dopamine?
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How many distinct loci were identified in the GWAS study conducted by the Schizophrenia Working Group of PGC?
How many distinct loci were identified in the GWAS study conducted by the Schizophrenia Working Group of PGC?
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What is the potential link between schizophrenia and immune system function suggested by the GWAS study?
What is the potential link between schizophrenia and immune system function suggested by the GWAS study?
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Which neurotransmitter's receptor genes were notably highlighted in the GWAS analysis?
Which neurotransmitter's receptor genes were notably highlighted in the GWAS analysis?
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What aspect of neuronal function is affected by genetic factors in individuals with schizophrenia?
What aspect of neuronal function is affected by genetic factors in individuals with schizophrenia?
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Which gene is thought to contribute to glutamatergic activity?
Which gene is thought to contribute to glutamatergic activity?
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What feature of the DISC1 gene is particularly significant to neuronal connectivity?
What feature of the DISC1 gene is particularly significant to neuronal connectivity?
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Study Notes
Schizophrenia Lecture 10
- Core Textbook Reading: Kalat, J.W. (2019). Biological Psychology, 13th edition. Boston, Massachusetts: Cengage Learning; Chapter 14: Module 14.3.
Aetiology of Schizophrenia
- Both genetic and environmental factors contribute to the cause of schizophrenia.
- Studies indicate a genetic predisposition to schizophrenia can be passed down.
- Research evidence for genetic transmission comes from family studies, twin studies, and adoption studies.
Twin Studies
- Concordance rates in identical twins (MZ) show a predisposition to schizophrenia is heritable.
- However, concordance rates are not 100%, proving environmental factors also play a crucial role.
- Some individuals can carry genes for schizophrenia but do not develop the disorder.
- Analyses of medical records (Norway and Denmark) support a genetic interpretation of high concordance rates in MZ twins.
- Gottesman & Bertelson (1989) research asks about children of discordant MZ twins, to understand risk of schizophrenia, considering twins eventually become parents.
- Data from MZ twins show children of twins without schizophrenia have similar risk as those with schizophrenia, but different rates were shown in DZ twins.
- These studies suggest genetic vulnerability that offspring inherit, even if individuals weren't diagnosed themselves.
- Twin studies have limitations - twins are not representative of the general population, experiencing different birth complications and varying mortality rates.
- Twins spend more time together and have similar social networks, increasing likelihood of shared environmental experiences, thus potentially confounding the results.
- Parental treatment differences exist between MZ and DZ twin pairs.
- All these factors lead to confounding environmental variables.
Large-scale Twin Study
- The large-scale Danish twin study (Hilker et al., 2018) reported concordance rates of 33% in MZ twins and 7% in DZ twins.
- Genetic heritability was estimated at 79%.
- The proband-wise method used in this study increases concordance rates, but it was criticized for the possibility to double-count cases
- The study highlights that only 15% of MZ twin pairs became concordant
- The 33% rate reported was a result of using this method partially.
- The modelling used to calculate genetic heritability in twin studies faces criticism (Torrey et al., 2019).
- The models rely on inaccurate assumptions – twins being similar to general populations and the same shared environment effects on both MZ & DZ pairs and minimal gene-environment interactions.
Adoption Studies
- Adoption studies examine adopted children who develop schizophrenia, which support a genetic basis for schizophrenia.
- Genetic and rearing factors can be analyzed in adoption studies.
- Hypothesis: Adults with schizophrenia adopted as children are more likely to have biological relatives with schizophrenia compared with those not affected.
- Kety (1994) compared relatives of adoptees with and without schizophrenia and found that first-degree biological relatives of adoptees with schizophrenia had a 12.5% rate of schizophrenia.
- This was corroborated by similarities in findings with other adoption studies with findings from Heston (1966) and Kety (1988)
- Tienari et al. (2004) did a long-term follow-up Finnish nationwide sample of adoptees.
- Families were studied for presence or absence of schizophrenia, comparing high and low genetic risk groups in family environments
- Clinical observations and interviews were used to understand family functioning by using the Oulu Family Rating Scale (OPAS)
- Tienari found a higher probability of schizophrenia among children with biological mothers with schizophrenia, but did not see the same in the low genetic risk group.
- The probability of schizophrenia was higher for children from mothers with schizophrenia and dysfunctional families.
Diathesis-Stress Model
- A model explaining increased susceptibility to schizophrenia by converging prenatal health issues with later stressors in adolescence/childhood.
Heritability of Schizophrenia
- Questions remain unanswered about the transmission, what is being inherited, genes related to the disorder and their control processes.
Efforts to Locate a Gene
- Schizophrenia is not caused by a single gene but likely multiple susceptibility genes with small effects, interacting with epigenetic and environmental factors (Cannon, 2015; Van Os & Kapur, 2009; Mueser & McGurk, 2004).
- Relevant genes include:
- COMT (catechol-O-methyltransferase) is involved in dopamine metabolism.
- G72 is thought to influence glutamatergic activity
- Neuregulin 1 is linked to NMDA, GABA, and ACh receptor regulation.
- Dysbindin influences presynaptic glutamate.
- DISC1 (disrupted in schizophrenia 1) gene impacts neuron differentiation and migration and also dendritic spine production and new neuron generation in the hippocampus.
GWAS Study
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An ambitious genome-wide association study (GWAS) by the Schizophrenia Working Group of the Psychiatric Genomics Consortium (2014) analyzed >35,000 individuals with schizophrenia and >110,000 controls.
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This identified 108 distinct loci, including 83 not previously linked to schizophrenia.
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Notable gene locations include genes for dopamine receptor D2 implicated in dopamine neurotransmission, genes for glutamatergic neurotransmission, and genes expressed in immune tissues, which supports a link between schizophrenia and the immune system.
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Ma et al. (2018) identified 6 crucial genes linked to increased schizophrenia risk, five relating to neurodevelopment.
In Summary
- Many genes are involved in schizophrenia, with small effects, and unknown transmission and expression (Coelewij & Curtis, 2018).
- A polygenic risk score can explain at least 7% of schizophrenia liability (Kendler, 2016).
- Around 5% of schizophrenia cases are linked to rare copy number variants (CNVs).
- Some CNVs significantly increase schizophrenia risk (Lowther et al., 2017).
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Description
This quiz covers the aetiology of schizophrenia as discussed in Lecture 10, focusing on the interplay between genetic and environmental factors. It highlights findings from twin studies and their implications for understanding the heritability of schizophrenia. Prepare to explore the complexities behind the genetic predisposition to this mental health disorder.
