Incidence of schizophrenia among second-generation immigrants in the jerusalem perinatal cohort

Lack of fit with the neighbourhood social environment as a risk factor for psychosis - a national cohort study

BACKGROUND

Many studies report an ethnic density effect whereby psychosis incidence among ethnic minority groups is higher in low co-ethnic density areas. It is unclear whether an equivalent density effect applies with other types of socioeconomic disadvantages.

METHODS

We followed a population cohort of 2 million native Danes comprising all those born on 1st January 1965, or later, living in Denmark on their 15th birthday. Socioeconomic disadvantage, based on parents' circumstances at age 15 (low income, manual occupation, single parent and unemployed), was measured alongside neighbourhood prevalence of these indices.

RESULTS

Each indicator was associated with a higher incidence of non-affective psychosis which remained the same, or was slightly reduced, if neighbourhood levels of disadvantage were lower. For example, for individuals from a low-income background there was no difference in incidence for those living in areas where a low-income was least common [incidence rate ratio (IRR) 1.01; 95% confidence interval (CI) 0.93-1.10 v. those in the quintile where a low income was most common. Typically, differences associated with area-level disadvantage were the same whether or not cohort members had a disadvantaged background; for instance, for those from a manual occupation background, incidence was lower in the quintile where this was least v. most common (IRR 0.83; 95% CI 0.71-0.97), as it was for those from a non-manual background (IRR 0.77; 95% CI 0.67-0.87).

CONCLUSION

We found little evidence for group density effects in contrast to previous ethnic density studies. Further research is needed with equivalent investigations in other countries to see if similar patterns are observed.

Effects of country of origin and wave of immigration on prevalence of schizophrenia among first and second-generation immigrants: A 30-year retrospective study

OBJECTIVES

To compare the rates of schizophrenia among 1st and 2nd generation immigrants from two distinct backgrounds and across sequential periods of immigration.

METHODS

A 30-years retrospective cohort study (187,184 individuals) of 1st and 2nd generation East-African immigrants (EAIs) and former Soviet-Union immigrants (FSUIs) who migrated to Israel between 1980 and 2012. EAIs were further divided according to waves of immigration. Period prevalence was calculated between the years 2002-2012. Multivariate logistic regression models were used to examine the association between immigration-related factors and prevalence of schizophrenia (Native-Born Israelis serving as reference group).

RESULTS

The prevalence of schizophrenia in 1st generation EAIs and FSUIs was 1.8% and 1.2%, respectively, compared to 1.0% among NBIs (p<0.001). The prevalence of schizophrenia among 2nd generation EAIs and FSUIs was 1.3% and 0.8%, respectively, compared to 0.6% among NBIs (p<0.001). Adjusted odds ratios for developing schizophrenia compared to NBIs were 1.6 (95%CI:1.4-1.8) and 2.1 (95%CI:1.6-2.7), among 1st and 2nd generation EAIs and 1.1 (95%CI:0.9-1.2) and 1.3 (95%CI:1.0-1.8) among 1st and 2nd generation FSUIs respectively. Among EAIs, we observed the highest rate of schizophrenia in the pioneer wave of immigrants with gradual decline across subsequent waves: 2.4%, 1.9% and 1.0% for the 1st, 2nd and 3rd waves of immigration, respectively (p<0.001).

CONCLUSIONS

The increased risk for developing schizophrenia among 2nd generation immigrants and among pioneer groups of immigrants emphasizes the importance of persistent investment in acculturation. Further studies elucidating the impact of country of origin and ethnic density on the risk for developing schizophrenia are warranted.

Equity in Mental Health Services for Youth at Clinical High Risk for Psychosis: Considering Marginalized Identities and Stressors

Prevention and early intervention programs have been initiated worldwide to serve youth at Clinical High Risk for Psychosis (CHR-P), who are adolescents and young adults experiencing subclinical psychosis and functional impairment. The primary goals of these efforts are to prevent or mitigate the onset of clinical psychosis, while also treating comorbid issues. It is important to consider issues of diversity, equity, and inclusion in CHR-P work, especially as these programs continue to proliferate around the world. Further, there is a long history in psychiatry of misdiagnosing and mistreating psychosis in individuals from racial and ethnic minority groups. Although there have been significant developments in early intervention psychosis work, there is evidence that marginalized groups are underserved by current CHR-P screening and intervention efforts. These issues are compounded by the contexts of continued social marginalization and significant mental health disparities in general child/adolescent services. Within this narrative review and call to action, we use an intersectional and minority stress lens to review and discuss current issues related to equity in CHR-P services, offer evidence-based recommendations, and propose next steps. In particular, our intersectional and minority stress lenses incorporate perspectives for a range of marginalized and underserved identities related to race, ethnicity, and culture; faith; immigration status; geography/residence; gender identity; sexual orientation; socioeconomic status/class; and ability status.

Migration and schizophrenia: meta-analysis and explanatory framework

Systematic reviews and meta-analyses suggest that there are increased rates of schizophrenia and related psychoses in first- and second-generation migrants and refugees. Here, we present a meta-analysis on the incidence of non-affective psychotic disorders among first- and second-generation migrants. We found substantial evidence for an increased relative risk of incidence among first- and second-generation migrants compared to the native population. As heterogeneity of included studies was high, effect estimates should be interpreted with caution and as guiding values rather than exact risk estimates. We interpret our findings in the context of social exclusion and isolation stress, and provide an explanatory framework that links cultural differences in verbal communication and experienced discrimination with the emergence of psychotic experiences and their neurobiological correlates. In this context, we discuss studies observing stress-dependent alterations of dopamine neurotransmission in studies among migrants versus non-migrants as well as in subjects with psychotic disorders. We suggest that social stress effects can impair contextualization of the meaning of verbal messages, which can be accounted for in Bayesian terms by a reduced precision of prior beliefs relative to sensory data, causing increased prediction errors and resulting in a shift towards the literal or "concrete" meaning of words. Compensatory alterations in higher-level beliefs, e.g., in the form of generalized interpretations of ambiguous interactions as hostile behavior, may contribute to psychotic experiences in migrants. We thus suggest that experienced discrimination and social exclusion is at the core of increased rates of psychotic experiences in subjects with a migration background.

Migration and psychosis: a meta-analysis of incidence studies

BACKGROUND

The aims of this meta-analysis are (i) to estimate the pooled relative risk (RR) of developing non-affective psychotic disorder (NAPD) and affective psychotic disorder (APD) among migrants and their children; (ii) to adjust these results for socioeconomic status (SES); (iii) to examine the sources of heterogeneity that underlie the risk of NAPD.

METHODS

We included population-based incidence studies that reported an age-adjusted RR with 95% confidence interval (CI) published 1 January 1977-12 October 2017 and used a random-effects model.

RESULTS

We retrieved studies performed in Europe (n = 43), Israel (n = 3), Canada (n = 2) and Australia (n = 1). The meta-analysis yielded a RR, adjusted for age and sex, of 2.13 (95% CI 1.99-2.27) for NAPD and 2.94 (95% CI 2.28-3.79) for APD. The RRs diminished, but persisted after adjustment for SES. With reference to NAPD: a personal or parental history of migration to Europe from countries outside Europe was associated with a higher RR (RR = 2.94, 95% CI 2.63-3.29) than migration within Europe (RR = 1.88, 95% 1.62-2.18). The corresponding RR was lower in Israel (RR = 1.22; 0.99-1.50) and Canada (RR = 1.21; 0.85-1.74). The RR was highest among individuals with a black skin colour (RR = 4.19, 95% CI 3.42-5.14). The evidence of a difference in risk between first and second generation was insufficient.

CONCLUSIONS

Positive selection may explain the low risk in Canada, while the change from exclusion to inclusion may do the same in Israel. Given the high risks among migrants from developing countries in Europe, social exclusion may have a pathogenic role.

Parental pre-conception stress status and risk for anxiety in rat offspring: specific and sex-dependent maternal and paternal effects

Prenatal stressful events have long-lasting consequences on behavioral responses of offspring. While the effects of gestational and maternal stress have been extensively studied on psychological alterations in the progeny, little is known about effects of each parent's pre-conception life events on emotional responses in offspring. Here, the effect of maternal and/or paternal pre-conception stress was investigated on anxiogenic responses of offspring. Male and female adult rats were subjected to predatory stress (contactless exposure to a cat for 1 + 1 h per day) for 50 (male, n: 12) and 15 (female, n: 24) consecutive days; controls were not exposed. After the stress procedure, the control and stressed rats were mated to create four types of breeding pairs: control female/control male, stressed female/control male, control female/stressed male, and stressed female/stressed male. On postnatal days 30-31, the offspring were tested on the elevated plus maze and plasma corticosterone concentration was measured. Half of the pups were exposed to acute predatory stress before the elevated plus maze test. In most subgroups, corticosterone and anxiety-like behaviors in the offspring with both or only one parent exposed to pre-gestational stress increased compared to their control counterparts. However, under acute stress conditions, a different sex-dependent pattern of anxiety responses emerged. The combined effects of maternal and paternal stress were not additive. Hence, individual offspring behaviors can be influenced by the former life stress experiences of either parent. Incorporation of genetic and epigenetic aspects in development of neurobehavioral abnormalities and reprograming of the hypothalamic-pituitary-adrenal axis may contribute to this phenomenon. Lay summary Early life stress (including during pregnancy) is known to have long-lasting effects on offspring, including emotional behaviors. Whether individual anxiety behaviors can be influenced by stress experiences of each parent even before a pregnancy is less well-understood. Our findings from this study on rats exposed to predator stress before mating suggest that maternal or paternal adult life events prior to pregnancy can lead to maladaptive behavior in their offspring later in life.

Psychoses sans Frontieres: towards an interdisciplinary understanding of psychosis risk amongst migrants and their descendants

Understanding the excess risk of psychotic disorders in migrant and ethnic minority groups has long been an important research focus in psychiatric epidemiology and public mental health. Heterogeneity between migrant groups based on the region of origin, minority status and other socioeconomic factors may provide clues as to the underlying aetiological mechanisms explaining this risk, as well as informing our general understanding of psychotic disorders. Nonetheless, disentangling the mechanisms underlying this association has been the focus of more speculation and theory to date than empirical research. Now more than ever, we need to move beyond studies which demonstrate excess rates in migrant and ethnic minority groups to novel population-based studies which identify the determinants and mechanisms through which this risk is shaped. In this paper, we review the main hypotheses proposed to explain these disparities and the current level of support for them. We then highlight recent evidence from epidemiology and neuroscience which provides important new clues in our understanding of the aetiology of psychotic disorders. We concluded with suggestions for future interdisciplinary research to prevent this public mental health inequality within a generation.

What do register-based studies tell us about migrant mental health? A scoping review

BACKGROUND

Previous studies investigating the mental health of migrants have shown mixed results. The increased availability of register data has led to a growing number of register-based studies in this research area. This is the first scoping review on the use of registry and record-linkage data to examine the mental health of migrant populations. The aim of this scoping review is to investigate the topics covered and to assess the results yielded from these studies.

METHODS

We used a scoping review methodology to search MedLine, PubMed, PsychINFO, Web of Science, and SCOPUS for all register-based studies on the mental health of migrants. Two reviewers screened all papers, independently, using iteratively applied inclusion and exclusion criteria. Using gradually broadening inclusion and exclusion criteria for maximum "scope," newly published criteria developed to appraise the methodological quality of record-linkage studies were applied to eligible papers and data were extracted in a charting exercise.

RESULTS

A total of 1309 papers were screened and appraised, 51 of which met the eligibility and quality criteria and were included in the review. This review identified four major domains of register-based research within the topic of migrant mental health: rates and risks of psychiatric disorders, rates and risks of suicide mortality, the use of psychotropic drugs, and health service utilisation and mental health-related hospitalisation rates. We found that whilst migrants can be at an increased risk of developing psychotic disorders and suicide mortality, they are less likely to use psychotropic medication and mental health-related services.

CONCLUSIONS

This review systematically charts the register-based studies on migrants' mental health for the first time. It shows the main topics and gaps in knowledge in this research domain, discusses the disadvantages of register-based studies, and suggests new directions for forthcoming studies.

Incidence of schizophrenia among migrants in the Netherlands: a direct comparison of first contact and longitudinal register approaches

PURPOSE

To estimate the effect of selective sampling on first contact (FC) studies of the relation between migration and schizophrenia.

METHODS

We compared the FC method directly with a more inclusive longitudinal psychiatric register (LPR) method, by letting both methods estimate age and sex adjusted incidence rate ratios (IRR) in the population of The Hague aged 20-54 years, for the three largest migrant groups (first and second generation Caribbean, Turkish, and Moroccan) relative to the native Dutch population.

RESULTS

Both methods found that the adjusted IRR was higher for migrants than for native Dutch [all migrants IRR = 1.70 (95% Cl 1.30-2.21) for the LPR method and 1.91 (95% Cl 1.15-3.25) for the FC]. The IRR for Moroccans was significantly lower in the LPR [IRR 2.69 (95% 2.10-3.41)] than in the FC study [4.81 (3.41-6.68)]. The FC method was relatively more inclusive for migrants presenting at earlier ages or with shorter durations of prior treatment (DPT) than the native Dutch. This resulted in differential sampling and artificially higher IRRs for Moroccan and, to a lesser extent, Turkish migrants.

CONCLUSION

We confirm that the incidence of schizophrenia is raised twofold for migrants compared to nonmigrants. Using the LPR method, however, IRR estimates were less pronounced for most migrant groups than in a high quality FC study conducted in the same population. The FC method may overestimate the risk of schizophrenia for migrant groups who seek first mental health at a relatively younger age, or who present directly with schizophrenia.

Does prenatal stress alter the developing connectome?

Human neurodevelopment requires the organization of neural elements into complex structural and functional networks called the connectome. Emerging data suggest that prenatal exposure to maternal stress plays a role in the wiring, or miswiring, of the developing connectome. Stress-related symptoms are common in women during pregnancy and are risk factors for neurobehavioral disorders ranging from autism spectrum disorder, attention deficit hyperactivity disorder, and addiction, to major depression and schizophrenia. This review focuses on structural and functional connectivity imaging to assess the impact of changes in women's stress-based physiology on the dynamic development of the human connectome in the fetal brain.

Immigration and psychotic experiences in the United States: Another example of the epidemiological paradox?

In Europe, it is widely established that immigration increases risk for psychotic disorder. However, research has yet to confirm this association in the United States, where immigrants paradoxically report better health status than their native-born counterparts. Further, few studies have examined this topic with respect to sub-threshold psychotic experiences, which are more common than psychotic disorders in the general population. This study analyzes the (1) National Comorbidity Survey-Replication, (2) the National Latino and Asian American Survey, and (3) the National Survey of American Life, in order to determine whether generation status had any impact on risk for lifetime and 12-month PE, and whether these associations vary across racial/ethnic groups, adjusting for demographic variables and socioeconomic status. We found an absence of an immigration effect on PE across various ethnic groups and across various geographic areas, and found that immigration is actually protective among Latinos, supporting the idea that the epidemiological paradox extends to the psychosis phenotype.

Common or distinct pathways to psychosis? A systematic review of evidence from prospective studies for developmental risk factors and antecedents of the schizophrenia spectrum disorders and affective psychoses

BACKGROUND

Identifying the unique and shared premorbid indicators of risk for the schizophrenia spectrum disorders (SSD) and affective psychoses (AP) may refine aetiological hypotheses and inform the delivery of universal versus targeted preventive interventions. This systematic review synthesises the available evidence concerning developmental risk factors and antecedents of SSD and AP to identify those with the most robust support, and to highlight remaining evidence gaps.

METHODS

A systematic search of prospective birth, population, high-risk, and case-control cohorts was conducted in Medline and supplemented by hand searching, incorporating published studies in English with full text available. Inclusion/exclusion decisions and data extraction were completed in duplicate. Exposures included three categories of risk factors and four categories of antecedents, with case and comparison groups defined by adult psychiatric diagnosis. Effect sizes and prevalence rates were extracted, where available, and the strength of evidence synthesised and evaluated qualitatively across the study designs.

RESULTS

Of 1775 studies identified by the search, 127 provided data to the review. Individuals who develop SSD experience a diversity of subtle premorbid developmental deficits and risk exposures, spanning the prenatal period through early adolescence. Those of greatest magnitude (or observed most consistently) included obstetric complications, maternal illness during pregnancy (especially infections), other maternal physical factors, negative family emotional environment, psychopathology and psychotic symptoms, and cognitive and motor dysfunctions. Relatively less evidence has accumulated to implicate this diversity of exposures in AP, and many yet remain unexamined, with the most consistent or strongest evidence to date being for obstetric complications, psychopathology, cognitive indicators and motor dysfunction. Among the few investigations affording direct comparison between SSD and AP, larger effect sizes and a greater number of significant associations are commonly reported for SSD relative to AP.

CONCLUSIONS

Shared risk factors for SSD and AP may include obstetric complications, childhood psychopathology, cognitive markers and motor dysfunction, but the capacity to distinguish common versus distinct risk factors/antecedents for SSD and AP is limited by the scant availability of prospective data for AP, and inconsistency in replication. Further studies considering both diagnoses concurrently are needed. Nonetheless, the prevalence of the risk factors/antecedents observed in cases and controls helps demarcate potential targets for preventative interventions for these disorders.

Incidence of psychotic disorders among first-generation immigrants and refugees in Ontario

BACKGROUND

Evidence suggests that migrant groups have an increased risk of psychotic disorders and that the level of risk varies by country of origin and host country. Canadian evidence is lacking on the incidence of psychotic disorders among migrants. We sought to examine the incidence of schizophrenia and schizoaffective disorders in first-generation immigrants and refugees in the province of Ontario, relative to the general population.

METHODS

We constructed a retrospective cohort that included people aged 14-40 years residing in Ontario as of Apr. 1, 1999. Population-based administrative data from physician billings and hospital admissions were linked to data from Citizenship and Immigration Canada. We used Poisson regression models to calculate age- and sex-adjusted incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for immigrant and refugee groups over a 10-year period.

RESULTS

In our cohort (n = 4,284,694), we found higher rates of psychotic disorders among immigrants from the Caribbean and Bermuda (IRR 1.60, 95% CI 1.29-1.98). Lower rates were found among immigrants from northern Europe (IRR 0.50, 95% CI 0.28-0.91), southern Europe (IRR 0.60, 95% CI 0.41-0.90) and East Asia (IRR 0.56, 95% CI 0.41-0.78). Refugee status was an independent predictor of risk among all migrants (IRR 1.27, 95% CI 1.04-1.56), and higher rates were found specifically for refugees from East Africa (IRR 1.95, 95% CI 1.44-2.65) and South Asia (IRR 1.51, 95% CI 1.08-2.12).

INTERPRETATION

The differential pattern of risk across ethnic subgroups in Ontario suggests that psychosocial and cultural factors associated with migration may contribute to the risk of psychotic disorders. Some groups may be more at risk, whereas others are protected.

The Concept of Schizophrenia: From Unity to Diversity

After over 100 years of research without clarifying the aetiology of schizophrenia, a look at the current state of knowledge in epidemiology, genetics, precursors, psychopathology, and outcome seems worthwhile. The disease concept, created by Kraepelin and modified by Bleuler, has a varied history. Today, schizophrenia is considered a polygenic disorder with onset in early adulthood, characterized by irregular psychotic episodes and functional impairment, but incident cases occur at all ages with marked differences in symptoms and social outcome. Men’s and women’s lifetime risk is nearly the same. At young age, women fall ill a few years later and less severely than men, men more rarely and less severely later in life. The underlying protective effect of oestrogen is antagonized by genetic load. The illness course is heterogeneous and depressive mood the most frequent symptom. Depression and schizophrenia are functionally associated, and affective and nonaffective psychoses do not split neatly. Most social consequences occur at the prodromal stage. Neither schizophrenia as such nor its main symptom dimensions regularly show pronounced deterioration over time. Schizophrenia is neither a residual state of a neurodevelopmental disorder nor a progressing neurodegenerative process. It reflects multifactorial CNS instability, which leads to cognitive deficits and symptom exacerbations.

Maternal stress induces epigenetic signatures of psychiatric and neurological diseases in the offspring

The gestational state is a period of particular vulnerability to diseases that affect maternal and fetal health. Stress during gestation may represent a powerful influence on maternal mental health and offspring brain plasticity and development. Here we show that the fetal transcriptome, through microRNA (miRNA) regulation, responds to prenatal stress in association with epigenetic signatures of psychiatric and neurological diseases. Pregnant Long-Evans rats were assigned to stress from gestational days 12 to 18 while others served as handled controls. Gestational stress in the dam disrupted parturient maternal behaviour and was accompanied by characteristic brain miRNA profiles in the mother and her offspring, and altered transcriptomic brain profiles in the offspring. In the offspring brains, prenatal stress upregulated miR-103, which is involved in brain pathologies, and downregulated its potential gene target Ptplb. Prenatal stress downregulated miR-145, a marker of multiple sclerosis in humans. Prenatal stress also upregulated miR-323 and miR-98, which may alter inflammatory responses in the brain. Furthermore, prenatal stress upregulated miR-219, which targets the gene Dazap1. Both miR-219 and Dazap1 are putative markers of schizophrenia and bipolar affective disorder in humans. Offspring transcriptomic changes included genes related to development, axonal guidance and neuropathology. These findings indicate that prenatal stress modifies epigenetic signatures linked to disease during critical periods of fetal brain development. These observations provide a new mechanistic association between environmental and genetic risk factors in psychiatric and neurological disease.

[Environmental risk factors for schizophrenia: a review]

BACKGROUND

Evidence of variations in schizophrenia incidence rates has been found in genetically homogenous populations, depending on changes within time or space of certain environmental characteristics. The consideration of the impact of environmental risk factors in etiopathogenic studies has put the environment in the forefront of research regarding psychotic illnesses. Various environmental factors such as urbanicity, migration, cannabis, childhood traumas, infectious agents, obstetrical complications and psychosocial factors have been associated with the risk of developing schizophrenia. These risk factors can be biological, physical, psychological as well as social and may operate at different times in an individual's life (fetal period, childhood, adolescence and early adulthood). Whilst some of these factors act on an individual level, others act on a populational level, modulating the individual risk. These factors can have a direct action on the development of schizophrenia, or on the other hand act as markers for directly implicated factors that have not yet been identified.

LITERATURE FINDINGS

This article summarizes the current knowledge on this subject. An extensive literature search was conducted via the search engine Pubmed. Eight risk factors were selected and developed in the following paper: urbanicity (or living in an urban area), cannabis, migration (and ethnic density), obstetrical complications, seasonality of birth, infectious agents (and inflammatory responses), socio-demographic factors and childhood traumas. For each of these factors, we provide information on the importance of the risk, the vulnerability period, hypotheses made on the possible mechanisms behind the factors and the level of proof the current research offers (good, medium, or insufficient) according to the amount, type, quality and concordance of the studies at hand. Some factors, such as cannabis, are "unique" in their influence on the development of schizophrenia since it labels only one risk factor. Others, such as obstetrical complications, are grouped (or "composed") in that they include various sub-factors that can influence the development of schizophrenia.

DISCUSSION

The data reviewed clearly demonstrates that environmental factors have an influence on the risk of developing schizophrenia. For certain factors - cannabis, migration, urbanicity, obstetrical complications, seasonality - there is enough evidence to establish an association with the risk of schizophrenia. This association, however, remains weak (especially for seasonality). With the exception of cannabis, no direct link can yet be established. Concerning the three remaining factors - childhood traumas, infectious agents, socio-demographic factors - the available proof is insufficient. One main limitation concerning all environmental factors is the generalization of results due to the fact that the studies were conducted on geographically limited populations. The current state of knowledge does not allow us to determine the mechanisms by which these factors may act.

CONCLUSION

Further research is needed to fill the gaps in our understanding of the subject. In response to this need, a collaborative European project (European Study of Gene-Environment Interactions [EU GEI]) was set-up. This study proposes the analysis of those environmental factors that influence the incidence of schizophrenia in various European countries, in both rural and urban settings, migrant and native populations, as well as their interaction with genetic factors.

Psychotic experiences: disadvantaged and different from the norm

Stress-induced alterations in how a person attributes meaning to internal and external stimuli may represent the first step in explaining how population ethnic minority-majority interactions affect mental health. Cross-context and diagnostic assumption-free research is required to elucidate how the wider social environment interacts with personal characteristics to increase expression of psychosis.

Risk of schizophrenia in relation to parental origin and genome-wide divergence

BACKGROUND

Second-generation immigrants have an increased risk of schizophrenia, a finding that still lacks a satisfactory explanation. Various operational definitions of second-generation immigrants have been used, including foreign parental country of birth. However, with increasing global migration, it is not clear that parental country of birth necessarily is informative with regard to ethnicity. We compare two independently collected measures of parental foreign ethnicity, parental foreign country of birth versus genetic divergence, based on genome-wide genotypic data, to access which measure most efficiently captures the increased risk of schizophrenia among second-generation immigrants residing in Denmark.

METHOD

A case-control study covering all children born in Denmark since 1981 included 892 cases of schizophrenia and 883 matched controls. Genetic divergence was assessed using principal component analyses of the genotypic data. Independently, parental foreign country of birth was assessed using information recorded prospectively in the Danish Civil Registration System. We compared incidence rate ratios of schizophrenia associated with these two independently collected measures of parental foreign ethnicity.

RESULTS

People with foreign-born parents had a significantly increased risk of schizophrenia [relative risk (RR) 1.94 (95% confidence intervals (CI) 1.41-2.65)]. Genetically divergent persons also had a significant increased risk [RR 2.43 (95% CI 1.55-3.82)]. Mutual adjustment of parental foreign country of birth and genetic divergence showed no difference between these measures with regard to their potential impact on the results.

CONCLUSIONS

In terms of RR of schizophrenia, genetic divergence and parental foreign country of birth are interchangeable entities, and both entities have validity with regard to identifying second-generation immigrants.

The impact of immigration on the development of adolescent schizophrenia

PROBLEM

Impact of immigration on the development of adolescent schizophrenia.

METHODS

The review of literature used Academic Search Premier, CINHAL, PsychINFO, PubMed, and MEDLINE databases to examine reasons given to immigration as a risk factor to adolescent schizophrenia.

FINDINGS

There is not a single factor or a group of related factors that could explain why the incidence of schizophrenia among immigrants is higher compared with natives of the host county.

CONCLUSION

Further inquiry into this phenomenon is needed to understand factors that increase the risk of schizophrenia among immigrant children and to help plan and implement strategies for prevention.

Incidence of schizophrenia and other psychoses in England, 1950-2009: a systematic review and meta-analyses

BACKGROUND

We conducted a systematic review of incidence rates in England over a sixty-year period to determine the extent to which rates varied along accepted (age, sex) and less-accepted epidemiological gradients (ethnicity, migration and place of birth and upbringing, time).

OBJECTIVES

To determine variation in incidence of several psychotic disorders as above.

DATA SOURCES

Published and grey literature searches (MEDLINE, PSycINFO, EMBASE, CINAHL, ASSIA, HMIC), and identification of unpublished data through bibliographic searches and author communication.

STUDY ELIGIBILITY CRITERIA

Published 1950-2009; conducted wholly or partially in England; original data on incidence of non-organic adult-onset psychosis or one or more factor(s) pertaining to incidence.

PARTICIPANTS

People, 16-64 years, with first -onset psychosis, including non-affective psychoses, schizophrenia, bipolar disorder, psychotic depression and substance-induced psychosis.

STUDY APPRAISAL AND SYNTHESIS METHODS

Title, abstract and full-text review by two independent raters to identify suitable citations. Data were extracted to a standardized extraction form. Descriptive appraisals of variation in rates, including tables and forest plots, and where suitable, random-effects meta-analyses and meta-regressions to test specific hypotheses; rate heterogeneity was assessed by the I²-statistic.

RESULTS

83 citations met inclusion. Pooled incidence of all psychoses (N = 9) was 31.7 per 100,000 person-years (95%CI: 24.6-40.9), 23.2 (95%CI: 18.3-29.5) for non-affective psychoses (N = 8), 15.2 (95%CI: 11.9-19.5) for schizophrenia (N = 15) and 12.4 (95%CI: 9.0-17.1) for affective psychoses (N = 7). This masked rate heterogeneity (I²: 0.54-0.97), possibly explained by socio-environmental factors; our review confirmed (via meta-regression) the typical age-sex interaction in psychosis risk, including secondary peak onset in women after 45 years. Rates of most disorders were elevated in several ethnic minority groups compared with the white (British) population. For example, for schizophrenia: black Caribbean (pooled RR: 5.6; 95%CI: 3.4-9.2; N = 5), black African (pooled RR: 4.7; 95%CI: 3.3-6.8; N = 5) and South Asian groups in England (pooled RR: 2.4; 95%CI: 1.3-4.5; N = 3). We found no evidence to support an overall change in the incidence of psychotic disorder over time, though diagnostic shifts (away from schizophrenia) were reported.

LIMITATIONS

Incidence studies were predominantly cross-sectional, limiting causal inference. Heterogeneity, while evidencing important variation, suggested pooled estimates require interpretation alongside our descriptive systematic results.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

Incidence of psychotic disorders varied markedly by age, sex, place and migration status/ethnicity. Stable incidence over time, together with a robust socio-environmental epidemiology, provides a platform for developing prediction models for health service planning.

Elaboration on the association between immigration and schizophrenia: a population-based national study disaggregating annual trends, country of origin and sex over 15 years

PURPOSE

Generally, immigrant status and male sex are separately documented to increase the risk of schizophrenia; although population-based risk trends by sex and immigration over time have not been examined. This study aims to examine the extent to which immigration acts as a risk factor for schizophrenia, delineated by origin, sex and year, using national population-based data over 15 years.

METHOD

Data on all first psychiatric admissions from 1978 to 1992 (n = 10,892) from the National Psychiatric Hospitalization Case Registry of the State of Israel were merged with aggregate national data from the Israeli Central Bureau of Statistics.

RESULTS

Compared to native-born Israelis, people who migrated prior to the age of 15 (n = 2,335) were at a greater risk of schizophrenia (n = 8,557; RR = 1.6, 95% CI = 1.53; 1.68), particularly those from Far Eastern (RR = 2.43, 95% CI = 1.91; 3.1) and Caribbean and South American (RR = 1.94, 95% CI = 1.51; 2.51) countries. Aggregate risk was higher among female than male immigrants and over the 15-year study immigration-related risk declined across the sexes.

CONCLUSION

The current findings replicate past research showing that immigrants, particularly from a social minority, as suggested by the social defeat-hypothesis, are at an increased risk of schizophrenia, and extend past findings to show that risk at least in Israel has decreased with time irrespective of sex.

Migration and psychotic disorders

The incidence of psychotic disorders is extremely high in several immigrant groups in Europe. This article describes the epidemiological evidence for increased incidence rates among immigrants compared with nonimmigrant populations and explores possible explanations for this excess risk. Potential causes not only involve factors acting at the level of the individual, but encompass the broader social context of neighborhoods and ethnic groups. Growing up and living in a disadvantaged ethnic minority position, characterized by a low social status, high degree of discrimination against the group and low neighborhood ethnic density, may lead to an increased risk of psychotic disorders, especially when individuals reject their minority status and when their social resources are insufficient to buffer the impact of adverse social experiences. Future research should refine measures of the social context, adopt a life-course perspective and should integrate social and neurobiological pathways.

A meta-analysis of the risk for psychotic disorders among first- and second-generation immigrants

BACKGROUND

There is increasing acceptance of migration as a risk factor for schizophrenia and related disorders; however, the magnitude of the risk among second-generation immigrants (SGIs) remains unclear. Generational differences in the incidence of psychotic disorders among migrants might improve our understanding of the relationship between migration, ethnicity and psychotic disorders. This meta-analysis aimed at determining the risk of psychotic disorders among SGIs in comparison with non-migrants and first-generation immigrants (FGIs).

METHOD

Medline, EMBASE and PsycINFO databases were searched systematically for population-based studies on migration and psychotic disorders published between 1977 and 2008. We also contacted experts, tracked citations and screened bibliographies. All potential publications were screened by two independent reviewers in a threefold process. Studies were included in the meta-analysis if they reported incidence data, differentiated FGIs from SGIs and provided age-adjusted data. Data extraction and quality assessment were conducted for each study.

RESULTS

Twenty-one studies met all inclusion criteria. A meta-analysis of 61 effect sizes for FGIs and 28 for SGIs yielded mean-weighted incidence rate ratios (IRRs) of 2.3 [95% confidence interval (CI) 2.0-2.7] for FGIs and 2.1 (95% CI 1.8-2.5) for SGIs. There was no significant risk difference between generations, but there were significant differences according to ethno-racial status and host country.

CONCLUSIONS

The increased risk of schizophrenia and related disorders among immigrants clearly persists into the second generation, suggesting that post-migration factors play a more important role than pre-migration factors or migration per se. The observed variability suggests that the risk is mediated by the social context.

Older paternal age strongly increases the morbidity for schizophrenia in sisters of affected females

The effect of a family history of schizophrenia on the risk for this disorder in the offspring has rarely been examined in a prospective population cohort accounting for the sex of the proband and the first-degree relatives, and certainly not with respect to later paternal age. The influence of affected relatives on offspring risk of schizophrenia was estimated using Cox proportional hazards regression in models that accounted for sex, relation of affected first degree relatives and paternal age in the prospective population-based cohort of the Jerusalem Perinatal Schizophrenia Study. Of all first-degree relatives, an affected mother conferred the highest risk to male and female offspring among the cases with paternal age <35 years, however, female offspring of fathers ≥35 years with an affected sister had the highest risk (RR = 8.8; 95% CI = 3.9-19.8). The risk seen between sisters of older fathers was fourfold greater than the risk to sisters of affected females of younger fathers (RR = 2.2, 95% CI 0.7-6.7). The test for interaction was significant (P = 0.03). By contrast, the risk of schizophrenia to brothers of affected males was only doubled between older (RR = 3.3, 95% 1.6-6.6) and younger fathers (RR = 1.6, 95% CI 0.7-3.5). The most striking finding from this study was the very large increase in risk of schizophrenia to sisters of affected females born to older fathers. The authors speculate that the hypothesized paternally expressed genes on the X chromosome might play some role in these observations.

Ethnic origin and increased risk for schizophrenia in immigrants to countries of recent and longstanding immigration

OBJECTIVES

Compare the risk for schizophrenia in immigrants to countries of recent and longstanding immigration. Compare prevalence and incidence rates in black subjects under different conditions.

METHOD

An electronic literature search was complemented by review articles and cross-references. Studies reporting standard diagnosis and incidence or prevalence rates were included.

RESULTS

Immigrants had an increased risk for schizophrenia in countries of longstanding immigration, but with lower risk ratios than in those of recent immigration. The risk was higher in black immigrants and the black population living in the United States. But incidence and prevalence rates in Africa and the Caribbean were similar to those of international studies.

CONCLUSION

Comparing the most recent generation of immigrants with descendants of previous ones may account for the lower risk ratios observed in countries of longstanding vs. recent immigration. Two neurobiological hypotheses are proposed to explain the epidemiological findings in black populations and in immigrants.

[Psychotic states in young migrants and children of migrants]

Psychiatric literature documenting increased rates of psychotic illness among migrants in European countries has been more and more reported during the past two decades. Social causes to this phenomenon have been highlighted. In this paper, we review and discuss this literature from the cultural psychiatry perspective. We can point three limitations to these works : the definition of the studied groups, the cultural validity diagnoses, and the psychic impact of migration and its complexity not being considered enough. The above considerations lead us to go forward with studies addressing this question. The need to construct methodologies addressing psychiatric epidemiology, transcultural psychiatry and human sciences is underlined.

Schizophrenia and birthplace of paternal and maternal grandfather in the Jerusalem perinatal cohort prospective study

Some forms of epigenetic abnormalities transmitted to offspring are manifested in differences in disease incidence that depend on parent-of-origin. To explore whether such phenomena might operate in schizophrenia spectrum disorders, we estimated the relative incidence of these conditions in relation to parent-of-origin by considering the two grandfathers' countries of birth. In a prospective cohort of 88,829 offspring, born in Jerusalem in 1964-76 we identified 637 cases through Israel's psychiatric registry. Relative risks (RR) were estimated for paternal and maternal grandfathers' countries of birth using proportional hazards methods, controlling for parents' ages, low social class and duration of marriage. After adjusting for multiple observations, we found no significant differences between descendants of maternal or paternal grandfathers born in Iraq, Iran, Turkey, Syria, Yemen, Morocco, Algeria, Tunisia, Libya/Egypt, Poland, USSR, Czechoslovakia, Germany or the USA. Those with paternal grandfathers from Romania (RR=1.9, 95% CI=1.3-2.8) or Hungary (1.6, 1.0-2.6) showed an increased incidence; however, those with maternal grandfathers from these countries experienced reduced incidence (RR=0.5, 0.3-0.8 and 0.4, 0.2-0.8). In post-hoc analyses we found that results were similar whether the comparison groups were restricted to descendants of other Europeans or included those from Western Asia and North Africa; and effects of paternal grandfathers from Romania/Hungary were more pronounced in females, while effects of maternal grandfathers from these countries were similar in males and females. These post-hoc "hypothesis-generating" findings lead one to question whether some families with ancestors in Romania or Hungary might carry a variant or mutation at a parentally imprinted locus that is altering susceptibility to schizophrenia. Such a locus, if it exists, might involve the X chromosome.

Effect of socioeconomic status and parents' education at birth on risk of schizophrenia in offspring

Although it is known that schizophrenia is associated with social class, controversy exists as to the nature of this association. The authors studied the incidence of schizophrenia in relation to social class at birth in a population-based cohort of 88,829 offspring born in Jerusalem in 1964-1976. They constructed a six-point scale to index social class, based on paternal occupation at the time of birth, with each of 108 occupations being ranked by mean education. Cox proportional hazards methods were used in adjusting for sex, parents' ages, duration of marriage and birth order. Linkage with Israel's Psychiatric Registry identified 637 people admitted to psychiatric care facilities with schizophrenia-related diagnoses, before 1998. There was no gradient of risk for schizophrenia associated with social class at birth; however, offspring of fathers in the lowest social class showed a modest increase in risk (adjusted Relative Risk = 1.4; 95% Confidence interval = 1.1-1.8, P = 0.002). These data suggest that in contrast to many other health outcomes, there is not a continuous gradient for increasing schizophrenia with decreasing social class of origin. Instead, a modest increase in risk for schizophrenia was observed only for those born at the bottom of the social ladder.