Schizophrenia and migration: a meta-analysis and review.
01 Jan 2005-American Journal of Psychiatry (American Psychiatric Association)-Vol. 162, Iss: 1, pp 12-24
TL;DR: Findings of previous studies implicating migration as a risk factor for the development of schizophrenia and a quantitative index of the associated effect size are synthesized to suggest a role for psychosocial adversity in the etiology of schizophrenia.
Abstract: OBJECTIVE: The authors synthesize findings of previous studies implicating migration as a risk factor for the development of schizophrenia and provide a quantitative index of the associated effect size. METHOD: MEDLINE was searched for population-based incidence studies concerning migrants in English-language publications appearing between the years 1977 and 2003. Article bibliographies and an Australian database were cross-referenced. Studies were included if incidence reports provided numerators and denominators and if age correction was performed or could be performed by the authors. Relative risks for migrant groups were extracted or calculated for each study. Significant heterogeneity across studies indicated the need for a mixed-effects meta-analytic model. RESULTS: The mean weighted relative risk for developing schizophrenia among first-generation migrants (40 effect sizes) was 2.7 (95% confidence interval [CI]=2.3–3.2). A separate analysis performed for second-generation migrants (seven effect siz...
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TL;DR: The dopamine hypothesis of schizophrenia-version III is synthesized into a comprehensive framework that links risk factors, including pregnancy and obstetric complications, stress and trauma, drug use, and genes, to increased presynaptic striatal dopaminergic function.
Abstract: The dopamine hypothesis of schizophrenia has been one of the most enduring ideas in psychiatry. Initially, the emphasis was on a role of hyperdopaminergia in the etiology of schizophrenia (version I), but it was subsequently reconceptualized to specify subcortical hyperdopaminergia with prefrontal hypodopaminergia (version II). However, these hypotheses focused too narrowly on dopamine itself, conflated psychosis and schizophrenia, and predated advances in the genetics, molecular biology, and imaging research in schizophrenia. Since version II, there have been over 6700 articles about dopamine and schizophrenia. We selectively review these data to provide an overview of the 5 critical streams of new evidence: neurochemical imaging studies, genetic evidence, findings on environmental risk factors, research into the extended phenotype, and animal studies. We synthesize this evidence into a new dopamine hypothesis of schizophrenia-version III: the final common pathway. This hypothesis seeks to be comprehensive in providing a framework that links risk factors, including pregnancy and obstetric complications, stress and trauma, drug use, and genes, to increased presynaptic striatal dopaminergic function. It explains how a complex array of pathological, positron emission tomography, magnetic resonance imaging, and other findings, such as frontotemporal structural and functional abnormalities and cognitive impairments, may converge neurochemically to cause psychosis through aberrant salience and lead to a diagnosis of schizophrenia. The hypothesis has one major implication for treatment approaches. Current treatments are acting downstream of the critical neurotransmitter abnormality. Future drug development and research into etiopathogenesis should focus on identifying and manipulating the upstream factors that converge on the dopaminergic funnel point.
2,311 citations
TL;DR: There is evidence, however, that transitory developmental expression of psychosis (psychosis proneness) may become abnormally persistent and subsequently clinically relevant (impairment), depending on the degree of environmental risk the person is additionally exposed to.
Abstract: A systematic review of all reported incidence and prevalence studies of population rates of subclinical psychotic experiences reveals a median prevalence rate of around 5% and a median incidence rate of around 3%. A meta-analysis of risk factors reveals associations with developmental stage, child and adult social adversity, psychoactive drug use, and also male sex and migrant status. The small difference between prevalence and incidence rates, together with data from follow-up studies, indicates that approximately 75-90% of developmental psychotic experiences are transitory and disappear over time. There is evidence, however, that transitory developmental expression of psychosis (psychosis proneness) may become abnormally persistent (persistence) and subsequently clinically relevant (impairment), depending on the degree of environmental risk the person is additionally exposed to. The psychosis proneness-persistence-impairment model considers genetic background factors impacting on a broadly distributed and transitory population expression of psychosis during development, poor prognosis of which, in terms of persistence and clinical need, is predicted by environmental exposure interacting with genetic risk.
1,946 citations
Cites background from "Schizophrenia and migration: a meta..."
...Some of the non-genetic risk factors associated with schizophrenia such as urbanicity (Krabbendam & van Os, 2005), ethnic minority status (Cantor-Graae & Selten, 2005), childhood trauma (Read et al. 2005) and cannabis (Henquet et al. 2005) may also impact on the rate of subclinical psychotic…...
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TL;DR: The aims of this review are to systematically identify and collate studies describing the prevalence of schizophrenia, to summarize the findings of these studies, and to explore selected factors that may influence prevalence estimates.
Abstract: Background Understanding the prevalence of schizophrenia has important implications for both health service planning and risk factor epidemiology. The aims of this review are to systematically identify and collate studies describing the prevalence of schizophrenia, to summarize the findings of these studies, and to explore selected factors that may influence prevalence estimates. Methods and Findings Studies with original data related to the prevalence of schizophrenia (published 1965–2002) were identified via searching electronic databases, reviewing citations, and writing to authors. These studies were divided into ‘‘core’’ studies, ‘‘migrant’’ studies, and studies based on ‘‘other special groups.’’ Between- and within-study filters were applied in order to identify discrete prevalence estimates. Cumulative plots of prevalence estimates were made and the distributions described when the underlying estimates were sorted according to prevalence type (point, period, lifetime, and lifetime morbid risk). Based on combined prevalence estimates, the influence of selected key variables was examined (sex, urbanicity, migrant status, country economic index, and study quality). A total of 1,721 prevalence estimates from 188 studies were identified. These estimates were drawn from 46 countries, and were based on an estimated 154,140 potentially overlapping prevalent cases. We identified 132 core studies, 15 migrant studies, and 41 studies based on other special groups. The median values per 1,000 persons (10%–90% quantiles) for the distributions for point, period, lifetime, and lifetime morbid risk were 4.6 (1.9–10.0), 3.3 (1.3– 8.2), 4.0 (1.6–12.1), and 7.2 (3.1–27.1), respectively. Based on combined prevalence estimates, we found no significant difference (a) between males and females, or (b) between urban, rural, and mixed sites. The prevalence of schizophrenia in migrants was higher compared to nativeborn individuals: the migrant-to-native-born ratio median (10%–90% quantile) was 1.8 (0.9–6.4). When sites were grouped by economic status, prevalence estimates from ‘‘least developed’’ countries were significantly lower than those from both ‘‘emerging’’ and ‘‘developed’’ sites (p = 0.04). Studies that scored higher on a quality score had significantly higher prevalence estimates ( p= 0.02).
1,824 citations
TL;DR: The epidemiology of schizophrenia is characterized by prominent variability and gradients that can help guide future research.
Abstract: Recent systematic reviews have encouraged the psychiatric research community to reevaluate the contours of schizophrenia epidemiology. This paper provides a concise overview of three related systematic reviews on the incidence, prevalence, and mortality associated with schizophrenia. The reviews shared key methodological features regarding search strategies, analysis of the distribution of the frequency estimates, and exploration of the influence of key variables (sex, migrant status, urbanicity, secular trend, economic status, and latitude). Contrary to previous interpretations, the incidence of schizophrenia shows prominent variation between sites. The median incidence of schizophrenia was 15.2/100,000 persons, and the central 80% of estimates varied over a fivefold range (7.7-43.0/100,000). The rate ratio for males:females was 1.4:1. Prevalence estimates also show prominent variation. The median lifetime morbid risk for schizophrenia was 7.2/1,000 persons. On the basis of the standardized mortality ratio, people with schizophrenia have a two- to threefold increased risk of dying (median standardized mortality ratio = 2.6 for all-cause mortality), and this differential gap in mortality has increased over recent decades. Compared with native-born individuals, migrants have an increased incidence and prevalence of schizophrenia. Exposures related to urbanicity, economic status, and latitude are also associated with various frequency measures. In conclusion, the epidemiology of schizophrenia is characterized by prominent variability and gradients that can help guide future research.
1,766 citations
Cites background from "Schizophrenia and migration: a meta..."
...For example, evidence suggests that the incidence of schizophrenia is related to sex (3), migrant status (30), and urbanicity (31–33)....
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...The association between migrant status and schizophrenia is one of the most startling gradients in schizophrenia epidemiology to emerge in recent decades (30)....
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TL;DR: A review of reviews to describe methods used to assess the quality of prognosis studies and to describe how well current practices assess potential biases is to develop recommendations to guide future quality appraisal.
Abstract: In examining how researchers assess the quality of individual studies in systematic reviews about prognosis, the authors found that appraisal of the quality of the article, a necessary step in syst...
1,298 citations
References
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TL;DR: The prevalence of psychiatric disorders is greater than previously thought to be the case, and morbidity is more highly concentrated than previously recognized in roughly one sixth of the population who have a history of three or more comorbid disorders.
Abstract: Background: This study presents estimates of lifetime and 12-month prevalence of 14 DSM-III-R psychiatric disorders from the National Comorbidity Survey, the first survey to administer a structured psychiatric interview to a national probability sample in the United States. Methods: The DSM-III-R psychiatric disorders among persons aged 15 to 54 years in the noninstitutionalized civilian population of the United States were assessed with data collected by lay interviewers using a revised version of the Composite International Diagnostic Interview. Results: Nearly 50% of respondents reported at least one lifetime disorder, and close to 30% reported at least one 12-month disorder. The most common disorders were major depressive episode, alcohol dependence, social phobia, and simple phobia. More than half of all lifetime disorders occurred in the 14% of the population who had a history of three or more comorbid disorders. These highly comorbid people also included the vast majority of people with severe disorders. Less than 40% of those with a lifetime disorder had ever received professional treatment, and less than 20% of those with a recent disorder had been in treatment during the past 12 months. Consistent with previous risk factor research, it was found that women had elevated rates of affective disorders and anxiety disorders, that men had elevated rates of substance use disorders and antisocial personality disorder, and that most disorders declined with age and with higher socioeconomic status. Conclusions: The prevalence of psychiatric disorders is greater than previously thought to be the case. Furthermore, this morbidity is more highly concentrated than previously recognized in roughly one sixth of the population who have a history of three or more comorbid disorders. This suggests that the causes and consequences of high comorbidity should be the focus of research attention. The majority of people with psychiatric disorders fail to obtain professional treatment. Even among people with a lifetime history of three or more comorbid disorders, the proportion who ever obtain specialty sector mental health treatment is less than 50%. These results argue for the importance of more outreach and more research on barriers to professional help-seeking.
11,648 citations
Book•
18 Aug 2000TL;DR: This paper presents a meta-analysis procedure called “Meta-Analysis Interpretation for Meta-Analysis Selecting, Computing and Coding the Effect Size Statistic and its applications to Data Management Analysis Issues and Strategies.
Abstract: Introduction Problem Specification and Study Retrieval Selecting, Computing and Coding the Effect Size Statistic Developing a Coding Scheme and Coding Study Reports Data Management Analysis Issues and Strategies Computational Techniques for Meta-Analysis Data Interpreting and Using Meta-Analysis Results
6,930 citations
"Schizophrenia and migration: a meta..." refers methods in this paper
...org is the number of migrant cases (derived from the formula for the variance of odds ratios) (22), as previously done by Aleman et al....
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TL;DR: Despite evidence of heterogeneity across studies, meta-analytic results from 12 published twin studies of schizophrenia are consistent with a view of schizophrenia as a complex trait that results from genetic and environmental etiological influences.
Abstract: Context There are many published twin studies of schizophrenia. Although these studies have been reviewed previously, to our knowledge, no review has provided quantitative summary estimates of the impact of genes and environment on liability to schizophrenia that also accounted for the different ascertainment strategies used. Objective To calculate meta-analytic estimates of heritability in liability and shared and individual-specific environmental effects from the pooled twin data. Data Sources We used a structured literature search to identify all published twin studies of schizophrenia, including MEDLINE, dissertation, and books-in-print searches. Study Selection Of the 14 identified studies, 12 met the minimal inclusion criteria of systematic ascertainment. Data Synthesis By using a multigroup twin model, we found evidence for substantial additive genetic effects—the point estimate of heritability in liability to schizophrenia was 81% (95% confidence interval, 73%-90%). Notably, there was consistent evidence across these studies for common or shared environmental influences on liability to schizophrenia—joint estimate, 11% (95% confidence interval, 3%-19%). Conclusions Despite evidence of heterogeneity across studies, these meta-analytic results from 12 published twin studies of schizophrenia are consistent with a view of schizophrenia as a complex trait that results from genetic and environmental etiological influences. These results are broadly informative in that they provide no information about the specific identity of these etiological influences, but they do provide a component of a unifying empirical basis supporting the rationality of searches for underlying genetic and common environmental etiological factors.
2,100 citations
"Schizophrenia and migration: a meta..." refers background in this paper
...Nevertheless, meta-analytical evidence from twin studies indicates that schizophrenia has complex multifactorial determinants that would include environmental factors (51)....
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TL;DR: The cognitive processes that are thought to lead to the formation and maintenance of the positive symptoms of psychosis are set out and a fuller integration with the findings of biological research will be required.
Abstract: In the last 10 years a consensus has developed that the symptoms of psychosis may be better understood by linking the steps between the phenomenological experiences and social, psychological and neurobiological levels of explanation. Cognitive models of psychosis are an important link in this chain. They provide a psychological description of the phenomena from which hypotheses concerning causal processes can be derived and tested; social, individual, and neurobiological factors can then be integrated via their impact on these cognitive processes. In this paper, we set out the cognitive processes that we think lead to the formation and maintenance of the positive symptoms of psychosis and we attempt to integrate into our model research in social factors. If this model proves useful, a fuller integration with the findings of biological research will be required (Frith, 1992).
1,419 citations
"Schizophrenia and migration: a meta..." refers background in this paper
...Experiences of discrimination may foster a paranoid attributional style that facilitates the development of psychotic symptoms (69)....
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TL;DR: Differences between children destined to develop schizophrenia as adults and the general population were found across a range of developmental domains, and the origins of schizophrenia may be found in early life.
1,326 citations