Sukanta Saha

A Systematic Review of the Prevalence of Schizophrenia

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 native-born 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). Conclusions There is a wealth of data about the prevalence of schizophrenia. These gradients, and the variability found in prevalence estimate distributions, can provide direction for future hypothesis-driven research.

Schizophrenia: A Concise Overview of Incidence, Prevalence, and Mortality

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.

A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology

BackgroundUnderstanding variations in the incidence of schizophrenia is a crucial step in unravelling the aetiology of this group of disorders. The aims of this review are to systematically identify studies related to the incidence of schizophrenia, to describe the key features of these studies, and to explore the distribution of rates derived from these studies.MethodsStudies with original data related to the incidence of schizophrenia (published 1965–2001) were identified via searching electronic databases, reviewing citations and writing to authors. These studies were divided into core studies, migrant studies, cohort studies and studies based on Other Special Groups. Between- and within-study filters were applied in order to identify discrete rates. Cumulative plots of these rates were made and these distributions were compared when the underlying rates were sorted according to sex, urbanicity, migrant status and various methodological features.ResultsWe identified 100 core studies, 24 migrant studies, 23 cohort studies and 14 studies based on Other Special Groups. These studies, which were drawn from 33 countries, generated a total of 1,458 rates. Based on discrete core data for persons (55 studies and 170 rates), the distribution of rates was asymmetric and had a median value (10%–90% quantile) of 15.2 (7.7–43.0) per 100,000. The distribution of rates was significantly higher in males compared to females; the male/female rate ratio median (10%–90% quantile) was 1.40 (0.9–2.4). Those studies conducted in urban versus mixed urban-rural catchment areas generated significantly higher rate distributions. The distribution of rates in migrants was significantly higher compared to native-born; the migrant/native-born rate ratio median (10%–90% quantile) was 4.6 (1.0–12.8). Apart from the finding that older studies reported higher rates, other study features were not associated with significantly different rate distributions (e.g. overall quality, methods related to case finding, diagnostic confirmation and criteria, the use of age-standardization and age range).ConclusionsThere is a wealth of data available on the incidence of schizophrenia. The width and skew of the rate distribution, and the significant impact of sex, urbanicity and migrant status on these distributions, indicate substantial variations in the incidence of schizophrenia.

A Systematic Review and Meta-Analysis of Recovery in Schizophrenia

OBJECTIVE Our primary aims were (a) to identify the proportion of individuals with schizophrenia and related psychoses who met recovery criteria based on both clinical and social domains and (b) to examine if recovery was associated with factors such as gender, economic index of sites, and selected design features of the study. We also examined if the proportions who met our definition of recovery had changed over time. METHOD A comprehensive search strategy was used to identify potential studies, and data were extracted for those that met inclusion criteria. The proportion who met our recovery criteria (improvements in both clinical and social domains and evidence that improvements in at least 1 of these 2 domains had persisted for at least 2 years) was extracted from each study. Meta-regression techniques were used to explore the association between the recovery proportions and the selected variables. RESULTS We identified 50 studies with data suitable for inclusion. The median proportion (25%-75% quantiles) who met our recovery criteria was 13.5% (8.1%-20.0%). Studies from sites in countries with poorer economic status had higher recovery proportions. However, there were no statistically significant differences when the estimates were stratified according to sex, midpoint of intake period, strictness of the diagnostic criteria, duration of follow-up, or other design features. CONCLUSIONS Based on the best available data, approximately, 1 in 7 individuals with schizophrenia met our criteria for recovery. Despite major changes in treatment options in recent decades, the proportion of recovered cases has not increased.

Advanced paternal age is associated with impaired neurocognitive outcomes during infancy and childhood

Background Advanced paternal age (APA) is associated with an increased risk of neurodevelopmental disorders such as autism and schizophrenia, as well as with dyslexia and reduced intelligence. The aim of this study was to examine the relationship between paternal age and performance on neurocognitive measures during infancy and childhood. Methods and Findings A sample of singleton children (n = 33,437) was drawn from the US Collaborative Perinatal Project. The outcome measures were assessed at 8 mo, 4 y, and 7 y (Bayley scales, Stanford Binet Intelligence Scale, Graham-Ernhart Block Sort Test, Wechsler Intelligence Scale for Children, Wide Range Achievement Test). The main analyses examined the relationship between neurocognitive measures and paternal or maternal age when adjusted for potential confounding factors. Advanced paternal age showed significant associations with poorer scores on all of the neurocognitive measures apart from the Bayley Motor score. The findings were broadly consistent in direction and effect size at all three ages. In contrast, advanced maternal age was generally associated with better scores on these same measures. Conclusions The offspring of older fathers show subtle impairments on tests of neurocognitive ability during infancy and childhood. In light of secular trends related to delayed fatherhood, the clinical implications and the mechanisms underlying these findings warrant closer scrutiny.

A systematic review of the association between common single nucleotide polymorphisms and 25-hydroxyvitamin D concentrations ☆

In order to appreciate the association between hypovitaminosis D and various adverse health outcomes, we require a thorough understanding of how common single nucleotide polymorphisms (SNPs) influence serum concentrations of 25-hydroxyvitamin D (25OHD). We undertook a systematic review of the literature in order to identify studies that examined 25OHD concentrations, and common SNPs. We found nine studies related to the vitamin D binding protein (group-specific component, GC), and five studies examining the vitamin D receptor (VDR). SNPs in a range of cytochrome P450 enzymes have also been examined in seven studies. Replicated findings have been found between 25OHD concentrations and (a) two SNPs in GC (rs4588, rs7041), (b) one SNP in VDR (rs10735810), and (c) one SNP in CYP27B1 (rs10877012). In light of these associations, it is feasible that optimal concentrations of 25OHD required to reduce disease outcomes may vary according to genotype. We speculate that recently identified U-shaped relationships between 25OHD concentrations and disease outcomes (i.e. increased risk at both high and low concentrations) may reflect a mixture of genotype-defined subgroups. Further research is required in order to clarify the genetic architecture underlying 25OHD serum concentrations, and to unravel the mechanisms of action responsible for these associations.

Psychotic Experiences in the General Population: A Cross-National Analysis Based on 31 261 Respondents From 18 Countries

IMPORTANCE Community-based surveys find that many otherwise healthy individuals report histories of hallucinations and delusions. To date, most studies have focused on the overall lifetime prevalence of any of these psychotic experiences (PEs), which might mask important features related to the types and frequencies of PEs. OBJECTIVE To explore detailed epidemiologic information about PEs in a large multinational sample. DESIGN, SETTING, AND PARTICIPANTS We obtained data from the World Health Organization World Mental Health Surveys, a coordinated set of community epidemiologic surveys of the prevalence and correlates of mental disorders in representative household samples from 18 countries throughout the world, from 2001 through 2009. Respondents included 31,261 adults (18 years and older) who were asked about lifetime and 12-month prevalence and frequency of 6 types of PEs (2 hallucinatory experiences and 4 delusional experiences). We analyzed the data from March 2014 through January 2015. MAIN OUTCOMES AND MEASURES Prevalence, frequency, and correlates of PEs. RESULTS Mean lifetime prevalence (SE) of ever having a PE was 5.8% (0.2%), with hallucinatory experiences (5.2% [0.2%]) much more common than delusional experiences (1.3% [0.1%]). More than two-thirds (72.0%) of respondents with lifetime PEs reported experiencing only 1 type. Psychotic experiences were typically infrequent, with 32.2% of respondents with lifetime PEs reporting only 1 occurrence and 31.8% reporting only 2 to 5 occurrences. We found a significant relationship between having more than 1 type of PE and having more frequent PE episodes (Cochran-Armitage z = -10.0; P < .001). Lifetime prevalence estimates (SEs) were significantly higher among respondents in middle- and high-income countries than among those in low-income countries (7.2% [0.4%], 6.8% [0.3%], and 3.2% [0.3%], respectively; χ²₂ range, 7.1-58.2; P < .001 for each) and among women than among men (6.6% [0.2%] vs 5.0% [0.3%]; χ²₁ = 16.0; P < .001). We found significant associations with lifetime prevalence of PEs in the multivariate model among nonmarried compared with married respondents (χ²₂ = 23.2; P < .001) and among respondents who were not employed (χ²₄= 10.6; P < .001) and who had low family incomes (χ²₃ = 16.9; P < .001). CONCLUSIONS AND RELEVANCE The epidemiologic features of PEs are more nuanced than previously thought. Research is needed that focuses on similarities and differences in the predictors of the onset, course, and consequences of distinct PEs.

Paternal and maternal age as risk factors for psychosis: findings from Denmark, Sweden and Australia

BACKGROUND While the association between increased maternal age and congenital disorders has long been recognized, the offspring of older fathers are also at increased risk of congenital disorders related to DNA errors during spermatogenesis. Recent studies have drawn attention to an association between increased paternal age and increased risk of schizophrenia. The aim of the current study was to examine both paternal and maternal age as risk factors for the broader category of psychosis. METHOD We used data from three sources examining psychosis: a population-based cohort study (Denmark), and two case-control studies (Sweden and Australia). RESULTS When controlling for the effect of maternal age, increased paternal age was significantly associated with increased risk of psychosis in the Danish and Swedish studies. The Australian study found no association between adjusted paternal age and risk of psychosis. When controlling for the effect of paternal age, younger maternal age was associated with an increased risk of psychoses in the Danish study alone. CONCLUSIONS The offspring of older fathers are at increased risk of developing psychosis. The role of paternally derived mutations and/or psychosocial factors associated with older paternal age warrants further research.

Meta-analyses of the incidence and prevalence of schizophrenia: conceptual and methodological issues

While meta‐analytic techniques are routine in the synthesis of data from randomized controlled trials, there are no clear guidelines on how best to summarize frequency data such as incidence and prevalence estimates. Based on data from two recent systematic reviews of the incidence and prevalence of schizophrenia, this paper explores some of the conceptual and methodological issues related to the meta‐analyses of frequency estimates in epidemiology. Because variations in the incidence and prevalence of disorders such as schizophrenia can be informative, there is a case against collapsing data into one pooled estimate. Variations in frequency estimates can be displayed graphically, or summarized with quantiles around measures of central tendency. If pooled estimated are of interest, then researchers need to be aware that studies based on large samples will leverage greater weight on the pooled value. Based on systematic reviews of the incidence and prevalence of schizophrenia, we explore if these and related issues are of practical concern. When used with appropriate caution, meta‐analysis can complement the synthesis of frequency data in epidemiology; however, researchers interested in variation should not rely on meta‐analysis alone. Copyright

The incidence and prevalence of schizophrenia varies with latitude.

Objective:  The aim of this study was to examine the association between latitude and the incidence and prevalence of schizophrenia based on two recently published systematic reviews.