Early risk factors in schizophrenia: place and season of birth (original) (raw)
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Seasonality of birth in schizophrenia: the effect of regional population density
Schizophrenia …, 1997
It has been suggested that winter birth in urban areas may be associated with an increased risk of schizophrenia. Data on 4139 patients with a hospital diagnosis of schizophrenia were obtained from a survey of public departments of psychiatry in metropolitan France. Place of birth was classified according to the administrative subdivision of French territory into 95 ‘départements’. Density of population in the decade and in the département of birth was identified using successive census data. A 20% excess (OR, 1.20; 95% CI, 1.03–1.40; p = 0.02) of winter births (January–March) was found among patients born in highly densely populated areas (> 136 inhabitants/km2) compared to those born in other areas. These results suggest that seasonal early environmental risk factor(s) linked to schizophrenia predominantly operate in urban areas.
Invited Commentary: Taking the Search for Causes of Schizophrenia to a Different Level
American Journal of Epidemiology, 2006
In recent years, epidemiologists have established major variations in the incidence of schizophrenia and have begun to investigate the causes of these variations. The report by Pedersen and Mortensen (Am J Epidemiol 2006;163:971-8) in this issue of the Journal examines the contribution of family-level factors to the urban-rural difference in the incidence of schizophrenia. Their results suggest that familial life in urban environments confers some effect that persists after families move to rural settings. Taking these findings together with those of previous studies, it appears that factors operating at the level of the social context, the family, and the individual may all contribute to the urban-rural difference in schizophrenia incidence. This work exemplifies an integrative, multilevel approach to epidemiologic research that employs principles central to eco-epidemiology and other, similar frameworks.
American Journal of Epidemiology, 2006
Many studies have identified urban-rural differences in schizophrenia risk. Hypothetical underlying cause(s) may include toxic exposures, diet, infections, and selective migration. The authors investigated whether the underlying cause(s) responsible for the urban-rural differences were rooted in families or in individuals. Linking data from the Danish Civil Registration System and the Danish Psychiatric Central Register, a population-based cohort of 711,897 people aged 15 years or more was established. Overall, 2,720 persons developed schizophrenia during the period 1970-2001. The authors evaluated whether the nearest older sibling's place of birth had an independent effect on schizophrenia risk. If the cause(s) responsible for the urban-rural differences are rooted in individuals only, the nearest older sibling's place of birth should have no independent effect. In this analysis, the nearest older sibling's place of birth had an independent effect; among persons who lived in a rural area during their first 15 years of life, the relative risk was 1.59 (95% confidence interval: 1.10, 2.30) if their nearest older sibling had been born in the capital area as compared with a rural area. Some of the cause(s) responsible for the urban-rural differences in schizophrenia risk are rooted in families, but some might also be rooted in individuals.
Progress in Neuro-Psychopharmacology and Biological Psychiatry, 2011
Objective: Despite the fact that association between winter birth excess and schizophrenia in the northern Hemisphere is well established, possible sex or birth-cohort differences in this winter birth excess remain unclear. We aimed to evaluate sex and birth-cohort differences in the seasonal birth distribution of patients with schizophrenia or non-schizophrenic psychosis. Method: The sample included 321 ICD-10 schizophrenia and 294 non-schizophrenic psychosis patients consecutively admitted into a psychiatric hospitalization unit in Granada, southern Spain, during a nine-year period (1998-2006). The distribution of births among the general population born over the same period as the patients was calculated. Results: Among schizophrenia males (n = 258), it was possible to demonstrate that the observed proportion of winter birth (December, January or February) was significantly higher than expected. Among schizophrenia females (n = 63), although proportions were as in males and the effect size of the difference between observed and expected winter births was not lower than for men, only a statistical trend could be demonstrated. Among patients with non-schizophrenic psychosis, the observed proportion of winter birth was significantly higher than expected in women, but not in men. The sex-adjusted proportion of winter birth among schizophrenia patients born in the 1940's (a time period characterized by poor economy and widespread food restrictions because of the Spanish post-civil-war period) was significantly higher than among those born later; a difference that does not occur among patients with a non-schizophrenic psychosis. Conclusions: Among schizophrenia patients born in winter there appear to be slight sex-differences and strong birth-cohort differences, possibly due to epidemiological factors such as poverty or maternal nutritional deprivation. Epidemiological findings related to winter birth excess among patients with schizophrenia must be identified in longitudinal studies.
Epidemiologia e psichiatria sociale
Many studies have identified urban-rural differences in schizophrenia risk. The underlying cause(s) may hypothetically include toxic exposures, diet, infections, and selective migration. In a recent study, we concluded that some of the cause(s) responsible for the urban-rural differences in schizophrenia risk are rooted in families, but some might also be rooted in individuals. First, we describe temporality as a potential methodological pitfall within this line of research, then we review studies not subject to this pitfall, and finally, we describe why factors rooted in the family may solely explain the urban-rural differences. Although other potential explanations for these differences exist, we focus on this hypothesis as it has not previously been discussed in detail. To determine the cause(s) responsible for the urban-rural differences, we need direct measurements of genetic and/or environmental factors related to urban life.
Comments on risk for schizophrenia
Schizophrenia research, 2005
Recent developments have significantly furthered understanding of genetic and environmental factors affecting risk for schizophrenia. Environmental effects, such as immigration, living in a city, and substance abuse have been found to be associated with later schizophrenia. Although the highest risk for schizophrenia is still having a monozygotic twin with schizophrenia (50%), the candidate genes claimed to be associated to date only yield a very small excess risk and all of these effects (environmental and genetics) increase the risk for schizophrenia by only 2-3 fold. Thus, given the low prevalence of the disorder in the general population (0.5-1%), they are not practical in predicting future illness. One possible strategy to make the currently known risk factors for schizophrenia more useful clinically is based on findings indicating that many of the genetic and environmental risks cited above are not specific for schizophrenia, but increase risk for psychopathology in general. A...
Translational Psychiatry, 2016
Neighborhood influences in the etiology of schizophrenia have been emphasized in a number of systematic reviews, but causality remains uncertain. To test the social drift hypothesis, we used three complementary genetically informed Swedish cohorts. First, we used nationwide Swedish data on approximately 760 000 full-and half-sibling pairs born between 1951 and 1974 and quantitative genetic models to study genetic and environmental influences on the overlap between schizophrenia in young adulthood and subsequent residence in socioeconomically deprived neighborhoods. Schizophrenia diagnoses were ascertained using the National Patient Registry. Second, we tested the overlap between childhood psychotic experiences and neighborhood deprivation in early adulthood in the longitudinal Twin Study of Child and Adolescent Development (TCHAD; n = 2960). Third, we investigated to what extent polygenic risk scores for schizophrenia predicted residence in deprived neighborhoods during late adulthood using the TwinGene sample (n = 6796). Sibling data suggested that living in deprived neighborhoods was substantially heritable; 65% (95% confidence interval (95% CI): 60-71%) of the variance was attributed to genetic influences. Although the correlation between schizophrenia and neighborhood deprivation was moderate in magnitude (r = 0.22; 95% CI: 0.20-0.24), it was entirely explained by genetic influences. We replicated these findings in the TCHAD sample. Moreover, the association between polygenic risk for schizophrenia and neighborhood deprivation was statistically significant (R 2 = 0.15%, P = 0.002). Our findings are primarily consistent with a genetic selection interpretation where genetic liability for schizophrenia also predicts subsequent residence in socioeconomically deprived neighborhoods. Previous studies may have overemphasized the relative importance of environmental influences in the social drift of schizophrenia patients. Clinical and policy interventions will therefore benefit from the future identification of potentially causal pathways between different dimensions of cognitive functions and socioeconomic trajectories derived from studies adopting family-based research designs.