Maternal exposure to influenza and paranoid schizophrenia

Systematic review and meta-analysis: Season of birth and schizophrenia risk

OBJECTIVE

Winter birth has been hypothesized to be associated with increased schizophrenia risk for nearly a century. Major hypotheses regarding the potential etiological risk factors for schizophrenia such as vitamin D deficiency and virus exposure in utero are predicated based on the observation that risk of schizophrenia is higher in children born in winter months.

METHODS

We conducted a systematic review and meta-analysis to examine the association between season and month of birth and risk of schizophrenia. We further investigated this relationship stratified by hemisphere.

RESULTS

Forty-three studies spanning 30 countries and territories and 440,039 individuals with schizophrenia were included in this meta-analysis. Winter births were associated with a small but statistically significant increased risk of schizophrenia (OR 1.05, 95 % CI 1.03-1.07, p < 0.0001) and summer births were associated with a small but statistically significant decreased risk of schizophrenia (OR 0.96, 95 % CI 0.94-0.98, p = 0.0001). Stratified subgroup analysis demonstrated no significant difference between hemispheres in the risk of schizophrenia for either winter or summer births.

CONCLUSIONS

Analysis using birth month data demonstrated a clear seasonal trend towards increased risk of schizophrenia being associated with winter birth months and decreased risk of schizophrenia in summer-to-fall months in the Northern but not Southern Hemisphere. These data suggest a small-but-substantial increased risk of schizophrenia in winter birth month. Further research needs to examine potential etiologic causes for this association.

Is Psychopathy a Mental Disorder or an Adaptation? Evidence From a Meta-Analysis of the Association Between Psychopathy and Handedness

Psychopathy has historically been conceptualized as a mental disorder, but there is growing evidence that it may instead be an alternative, adaptive life history strategy designed by natural selection. Although the etiology of mental disorders is not fully understood, one likely contributor is perturbations affecting neurodevelopment. Nonright-handedness is a sign of such perturbations, and therefore can be used to test these competing models. If psychopathy is a mental disorder, psychopaths should show elevated rates of nonright-handedness. However, an adaptive strategy perspective expects psychopaths to be neurologically healthy and therefore predicts typical rates of nonright-handedness. We meta-analyzed 16 studies that investigated the association between psychopathy and handedness in various populations. There was no difference in the rates of nonright-handedness between community participants high and low in psychopathy. Furthermore, there was no difference between psychopathic and nonpsychopathic offenders in rates of nonright-handedness, though there was a tendency for offenders scoring higher on the Interpersonal/Affective dimension of psychopathy to have lower rates of nonright-handedness, and for offenders scoring higher on the Behavioral dimension of psychopathy to have higher rates of nonright-handedness. Lastly, there was no difference in rates of nonright-handedness between psychopathic and nonpsychopathic mental health patients. Thus, our results fail to support the mental disorder model and partly support the adaptive strategy model. We discuss limitations of the meta-analysis and implications for theories of the origins of psychopathy.

Human endogenous retrovirus type W (HERV-W) in schizophrenia: a new avenue of research at the gene-environment interface

OBJECTIVES

Provide a synthetic review of recent studies evidencing an association between human endogenous retrovirus-W (HERV-W) and schizophrenia.

METHODS

Bibliography analysis and contextual synthesis.

RESULTS

Epidemiological studies suggest that the aetiology of schizophrenia is complex and involves a complex interplay of genetic and environmental factors such as infections. Eight percentof the human genome consists of human endogenous retroviruses (HERV), and this part of the genome was previously thought to be without importance, but new research has refuted this. HERVs share similarities with viruses and it is assumed that HERVs are present in the genome as a result of retroviruses infecting germ line cells many million years ago. A specific type of HERVs, called HERV-W, has through several recent studies been associated with schizophrenia. Elevated transcription of HERV-W elements has been documented, and antigens of HERV-W envelope and capsid proteins have been found in blood samples from patients. Viruses that have been implicated in pathology of schizophrenia, such as herpes and influenza, have been shown to activate HERV-W elements, and such activation has been associated with elevated biomarkers of systemic inflammation. New research indicates that HERV-W may be an important genetic factor interplaying with the environmental risk factor of infections and that, through this, HERV-W may be important for disease pathogenesis.

CONCLUSIONS

A lifelong scenario of a detrimental interaction between infectious agents and HERV-W genes may decipher the actual development and course of schizophrenia. Further research is needed to find out if specific treatment strategies could reduce the expression of HERV-W and if this will be associated with remission.

The human endogenous retrovirus link between genes and environment in multiple sclerosis and in multifactorial diseases associating neuroinflammation

Endogenous retroviruses represent about 8% of the human genome and belong to the superfamily of transposable and retrotransposable genetic elements. Altogether, these mobile genetic elements and their numerous inactivated "junk" sequences represent nearly one half of the human DNA. Nonetheless, a significant part of this "non-conventional" genome has retained potential activity. Epigenetic control is notably involved in silencing most of these genetic elements but certain environmental factors such as viruses are known to dysregulate their expression in susceptible cells. More particularly, embryonal cells with limited gene methylation are most susceptible to uncontrolled activation of these mobile genetic elements by, e.g., viral infections. In particular, certain viruses transactivate promoters from endogenous retroviral family type W (HERV-W). HERV-W RNA was first isolated in circulating viral particles (Multiple Sclerosis-associated RetroViral element, MSRV) that have been associated with the evolution and prognosis of multiple sclerosis. HERV-W elements encode a powerful immunopathogenic envelope protein (ENV) that activates a pro-inflammatory and autoimmune cascade through interaction with Toll-like receptor 4 on immune cells. This ENV protein has repeatedly been detected in MS brain lesions and may be involved in other diseases. Epigenetic factors controlling HERV-W ENV protein expression then reveal critical. This review addresses the gene-environment epigenetic interface of such HERV-W elements and its potential involvement in disease.

Prenatal infection and schizophrenia: a review of epidemiologic and translational studies

An emerging literature from epidemiologic, clinical, and preclinical investigations has provided evidence that gestational exposure to infection contributes to the etiology of schizophrenia. In recent years, these studies have moved from ecologic designs, which ascertain infection based on epidemics in populations, to investigations that have capitalized on reliable biomarkers in individual pregnancies. These studies have documented specific candidate infections that appear to be associated with an elevated risk of schizophrenia. Animal models of maternal immune activation inspired by this work have revealed intriguing findings indicating behavioral, neurochemical, and neurophysiologic abnormalities consistent with observations in schizophrenia. In parallel studies in humans and animals, investigators are working to uncover the cellular and molecular mechanisms by which in utero exposure to infection contributes to schizophrenia risk. In this review, the authors discuss and critically evaluate the epidemiologic literature on in utero exposure to infection and schizophrenia, summarize emerging animal models of maternal immune activation, and discuss putative unique and common mechanisms by which in utero exposure to infection alters neurodevelopment, potentially increasing susceptibility to schizophrenia. The promise of this work for facilitating the identification of susceptibility loci in genetic studies of schizophrenia is illustrated by examples of interaction between in utero exposure to infection and genetic variants. The authors then elaborate on possible implications of this work, including the use of preventive measures for reducing the incidence of schizophrenia. Finally, they discuss new approaches aimed at addressing current challenges in this area of research.

Schizophrenia as a disorder of neurodevelopment

A combination of genetic susceptibility and environmental perturbations appear to be necessary for the expression of schizophrenia. In addition, the pathogenesis of the disease is hypothesized to be neurodevelopmental in nature based on reports of an excess of adverse events during the pre- and perinatal periods, the presence of cognitive and behavioral signs during childhood and adolescence, and the lack of evidence of a neurodegenerative process in most individuals with schizophrenia. Recent studies of neurodevelopmental mechanisms strongly suggest that no single gene or factor is responsible for driving a highly complex biological process. Together, these findings suggest that combinatorial genetic and environmental factors, which disturb a normal developmental course early in life, result in molecular and histogenic responses that cumulatively lead to different developmental trajectories and the clinical phenotype recognized as schizophrenia.

Seasonality and infectious disease in schizophrenia: the birth hypothesis revisited

Research literature supports the notion that more people diagnosed with schizophrenia are born during the winter months than other seasons [O'Hare A, Walsh D, Torrey F. Seasonality of schizophrenia births in Ireland. Br J Psychiatry 1980;137:74 7; Pulver AE, Stewart W, Carpenter WT, Jr., Childs B. Risk factors in schizophrenia: season of birth in Maryland, USA. Br J Psychiatry 1983;143:389-96.]. Researchers have postulated that this surge in winter-birth schizophrenia may be related to increases in viral infectious such as influenza and measles [Watson CG, Kucala T, Tilleskjor C, Jacobs L. Schizophrenic birth seasonality in relation to incidence of infectious diseases and temperature extremes. Arch Gen Psychiatry 1984:41:85-90; Mednick SA, Machon RA, Huttunen MO, Bonnett D. Adult schizophrenia following prenatal exposure to an influenza epidemic. Arch Gen Psychiatry 1988;45:189-92.]. However, data supporting significant relationships between infectious disease and schizophrenia incidence has been equivocal [Kendell R, Kemp I. Maternal influenza in the etiology of schizophrenia. Arch Gen Psychiatry 1989;46:878-82; McGrath J, Castle D. Does influenza cause schizophrenia? A five year review. Aust N Z J Psychiatry 1995;29:23-31.]. The purpose of this study was to replicate and expand previous studies by examining seasonal and infectious disease influences on schizophrenia prevalence. It was hypothesized that: (1) there would be an increase in schizophrenia prevalence during the winter months; and (2) that a significant amount of variability in schizophrenia birthrates would be accounted for by rates of influenza and measles. A Georgia Medicaid database (N = 746,615) and statewide infectious disease tables were used to identify correlations. Medicaid recipients were divided into schizophrenia (n = 11,736) and non-schizophrenia (n = 734,879) groups. A ratio of schizophrenic recipients to non-schizophrenic recipients was calculated for each birth cohort represented by each month of the year from 1948-1965. Multiple regression analyses indicated a significant relationship between winter season and schizophrenia incidence. However, neither influenza nor measles was predictive of schizophrenia prevalence. These findings were made using one of the largest sample of schizophrenic individuals in the literature to date. Limitations of the study are discussed, including the use of seasonal and prevalence correlations without data on patient linked maternal infections.

Prenatal exposure to the 1957 influenza pandemic and non-affective psychosis in The Netherlands

Second-trimester exposure to the 1957 A2 influenza pandemic is a controversial risk factor for schizophrenia. Two earlier studies of the Dutch psychiatric registry failed to find an increased risk for exposed subjects, but diagnostic misclassification within the spectrum of non-affective psychoses has not yet been ruled out as an explanation for the negative findings. Using an enlarged data-set we examined not only whether second-trimester exposure to the epidemic is associated with an increased risk of schizophrenia (ICD:295), but also whether it is associated with an increased risk of paranoid states (ICD:297) or other non-organic psychoses (ICD:298). In this retrospective cohort study the risks of the above-mentioned disorders were compared for those exposed and unexposed to A2 influenza during the second trimester of fetal life. The risks for the exposed subjects were not significantly higher than the risks for the unexposed. The power of the study to detect a significant increase in the risk of schizophrenia was sufficient. If the relative risk of a lifetime hospitalization for schizophrenia for second-trimester exposed subjects (born January-April 1958) is assumed to be 1.3, the power of the study would be 0.97 (alpha=0.05; one-tailed testing). If the relative risk for subjects born five months after the peak of the epidemic (mid-February to mid-March 1958) is assumed to be 1.88, as reported for England and Wales, the power of the study would be close to 1.00. This was the largest study of its kind in Europe: 275 subjects were born in the period January-April 1958 and had a lifetime hospitalization for schizophrenia. This study indicates that there is no relation between second-trimester exposure to the 1957 influenza pandemic and risk of non-affective psychosis in the Dutch population. It adds to a growing body of work which does not support an association between maternal influenza and schizophrenia.