Human leukocyte antigen and season of birth in Japanese patients with schizophrenia

Longitudinal analysis of proinflammatory and anti-inflammatory cytokines in the cerebrospinal fluid and peripheral blood of treatment-naïve first-episode psychosis patients, and their correlation with psychosis severity and cognitive impairment in sub-Saharan Africa

BACKGROUND

Inflammation is indicated as one of the factors that play a role in the development of schizophrenia, with several studies having found considerable inconsistencies in their results. Few have investigated the role of inflammation in primary psychosis in blood and cerebrospinal fluids simultaneously, the aim of this study being to investigate the expression of blood and cerebrospinal fluid inflammatory cytokines in treatment-naive first-episode psychotic participants.

METHODS AND ANALYSIS

This is a combined cross-sectional and prospective observational study, which is currently taking place in Durban, South Africa, will recruit 60 participants (30 cases and 30 matched controls). The primary objective is to describe baseline CSF and longitudinal expression/levels of inflammatory cytokines in the blood in persons diagnosed with first-episode psychosis (FEP) for 12 months. The secondary objective is to describe the associations between inflammatory cytokines and psychosis severity, neurocognitive performance, antipsychotic response and metabolic changes at different time points (baseline, 3, 6 and 12 months).

INTERVENTIONS

We will collect the sociodemographic details of all participants, and the Positive and Negative Symptoms Scale, Patient Health Questionnaire-9, Childhood Trauma Scale, Repeatable Battery for the Assessment of Neuropsychological Status Update, metabolic markers and inflammatory markers (venous blood and lumbar puncture cerebrospinal fluid) for those with FEP. Data from matched controls will only be collected at one point and no follow-ups (cross-sectional).

ETHICS AND DISSEMINATION

The study protocol has been approved by the University of KwaZulu-Natal Biomedical Research Ethics Committee (BREC/00004714/2022). The study is nested in an ongoing study titled the burden of HIV and Psychosis in an African setting: a longitudinal study of HIV-infected and non-infected patients with First-Episode Psychosis (BREC 571/18). The results will be actively disseminated through peer-reviewed journal publications and conference presentations.

Environmental Risk Factors for Schizophrenia and Bipolar Disorder and Their Relationship to Genetic Risk: Current Knowledge and Future Directions

Schizophrenia (SZ) and bipolar disorder (BD) are severe psychiatric disorders which result from complex interplay between genetic and environmental factors. It is well-established that they are highly heritable disorders, and considerable progress has been made identifying their shared and distinct genetic risk factors. However, the 15-40% of risk that is derived from environmental sources is less definitively known. Environmental factors that have been repeatedly investigated and often associated with SZ include: obstetric complications, infections, winter or spring birth, migration, urban living, childhood adversity, and cannabis use. There is evidence that childhood adversity and some types of infections are also associated with BD. Evidence for other risk factors in BD is weaker due to fewer studies and often smaller sample sizes. Relatively few environmental exposures have ever been examined for SZ or BD, and additional ones likely remain to be discovered. A complete picture of how genetic and environmental risk factors confer risk for these disorders requires an understanding of how they interact. Early gene-by-environment interaction studies for both SZ and BD often involved candidate genes and were underpowered. Larger samples with genome-wide data and polygenic risk scores now offer enhanced prospects to reveal genetic interactions with environmental exposures that contribute to risk for these disorders. Overall, although some environmental risk factors have been identified for SZ, few have been for BD, and the extent to which these account for the total risk from environmental sources remains unknown. For both disorders, interactions between genetic and environmental risk factors are also not well understood and merit further investigation. Questions remain regarding the mechanisms by which risk factors exert their effects, and the ways in which environmental factors differ by sex. Concurrent investigations of environmental and genetic risk factors in SZ and BD are needed as we work toward a more comprehensive understanding of the ways in which these disorders arise.

Interactions Between Variation in Candidate Genes and Environmental Factors in the Etiology of Schizophrenia and Bipolar Disorder: a Systematic Review

Schizophrenia and bipolar disorder (BD) are complex and multidimensional disorders with high heritability rates. The contribution of genetic factors to the etiology of these disorders is increasingly being recognized as the action of multiple risk variants with small effect sizes, which might explain only a minor part of susceptibility. On the other site, numerous environmental factors have been found to play an important role in their causality. Therefore, in recent years, several studies focused on gene × environment interactions that are believed to bridge the gap between genetic underpinnings and environmental insults. In this article, we performed a systematic review of studies investigating gene × environment interactions in BD and schizophrenia spectrum phenotypes. In the majority of studies from this field, interacting effects of variation in genes encoding catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF), and FK506-binding protein 5 (FKBP5) have been explored. Almost consistently, these studies revealed that polymorphisms in COMT, BDNF, and FKBP5 genes might interact with early life stress and cannabis abuse or dependence, influencing various outcomes of schizophrenia spectrum disorders and BD. Other interactions still require further replication in larger clinical and non-clinical samples. In addition, future studies should address the direction of causality and potential mechanisms of the relationship between gene × environment interactions and various categories of outcomes in schizophrenia and BD.

Seasonality of birth patterns in an Australian cohort of patients with biopsy-confirmed idiopathic inflammatory myopathy

Environmental exposures in the foetal period may predispose to autoimmunity. Aim of this study is to investigate whether seasonality in birth patterns exists in idiopathic inflammatory myopathies (IIM). We used Stata (StataCorp USA, version 13.0) and the user-written routine command 'circsummarise' to assess birth seasonality among South Australian patients with histologically confirmed IIM subsequent to 1980 using their date of birth. There was no evidence for a seasonal birth pattern among IIM patients overall (n = 568), however there were some ethnic variances in birth patterns among non-Caucasian patients. There was evidence for birth seasonality among both Aboriginal (mean = 7 July, Rayleigh P = 0.04) and Asian patients (mean = 12 August, Rayleigh P-value = 0.038). Non-Caucasians born in the third quarter of the calendar year may have an increased risk of developing IIM. Large international studies of IIM patients of diverse ethnicity are required to clarify the role of perinatal exposures in disease susceptibility.

Animal models of gene-environment interaction in schizophrenia: A dimensional perspective

Schizophrenia has long been considered as a disorder with multifactorial origins. Recent discoveries have advanced our understanding of the genetic architecture of the disease. However, even with the increase of identified risk variants, heritability estimates suggest an important contribution of non-genetic factors. Various environmental risk factors have been proposed to play a role in the etiopathogenesis of schizophrenia. These include season of birth, maternal infections, obstetric complications, adverse events at early childhood, and drug abuse. Despite the progress in identification of genetic and environmental risk factors, we still have a limited understanding of the mechanisms whereby gene-environment interactions (G × E) operate in schizophrenia and psychoses at large. In this review we provide a critical analysis of current animal models of G × E relevant to psychotic disorders and propose that dimensional perspective will advance our understanding of the complex mechanisms of these disorders.

Association of HLA-DR/DQ polymorphisms with schizophrenia in Tunisian patients

BACKGROUND AND OBJECTIVES

The hypothesis that human leukocyte antigens (HLAs) confer susceptibility to schizophrenic disorders has been tested by studying linkage and association in family samples. Our goal was to evaluate the role of HLA in the risk of developing schizophrenia in a Tunisian population.

DESIGN AND SETTINGS

Blood samples for this case-control study were collected from patients of the Department of Psychiatry at the Military Hospital of Tunisia between July 2012 and May 2013.

METHODS

A total of 140 patients with schizophrenia were recruited for genetic analysis. Controls included 100 persons matched for age, sex, and risk factors. Participants were tested for HLA class II alleles. HLA-DRB1 and HLA-DQB1 alleles were genotyped using polymerase chain reaction sequence-specific primers.

RESULTS

This study indicates that the alleles most responsible for disease susceptibility are DRB1*03 (P < 10-3) and DQB1*02 (P < 10-3) (P denotes probability values). The most protective alleles are DRB1*13 (P=.013) and DQB1*05 (P < 10-3). Further results revealed that DRB1*0301/DQB1*0201(P < 10-3), DRB1*0401/DQB1*0301 (P < 10-3) and DRB1*1101/DQB1*0301 (P < 10-3) are haplotypes most conducive to disease susceptibility.

CONCLUSION

The present findings support an association between schizophrenia and the HLA-DR-DQ locus among a Tunisian population. To our knowledge, this is the first study performed to analyze the association of HLA DRB1/DQB1 alleles on schizophrenia susceptibility in Tunisia.

The emerging molecular architecture of schizophrenia, polygenic risk scores and the clinical implications for GxE research

Schizophrenia is a devastating mental disorder. The level of risk in the general population is sustained by the persistence of social, environmental and biological factors, as well as their interactions. Socio-environmental risk factors for schizophrenia are well established and robust. The same can belatedly be said of genetic risk factors for the disorder. Recent progress in schizophrenia genetics is primarily fuelled by genome-wide association, which is able to leverage substantial proportions of additional explained variance previously classified as 'missing'. Here, we provide an outline of the emerging genetic landscape of schizophrenia and demonstrate how this knowledge can be turned into a simple empirical measure of genetic risk, known as a polygenic risk score. We highlight the statistical framework used to assess the clinical potential of the new score and finally, draw relevance to and discuss the clinical implications for the study of gene-environment interaction.

Molecular genetic gene-environment studies using candidate genes in schizophrenia: a systematic review

The relatively high heritability of schizophrenia suggests that genetic factors play an important role in the etiology of the disorder. On the other hand, a number of environmental factors significantly influence its incidence. As few direct genetic effects have been demonstrated, and there is considerable inter-individual heterogeneity in the response to the known environmental factors, interactions between genetic and environmental factors may be important in determining whether an individual develops the disorder. To date, a considerable number of studies of gene-environment interactions (G×E) in schizophrenia have employed a hypothesis-based molecular genetic approach using candidate genes, which have led to a range of different findings. This systematic review aims to summarize the results from molecular genetic candidate studies and to review challenges and opportunities of this approach in psychosis research. Finally, we discuss the potential of future prospects, such as new studies that combine hypothesis-based molecular genetic candidate approaches with agnostic genome-wide association studies in determining schizophrenia risk.

Variation in the major histocompatibility complex [MHC] gene family in schizophrenia: associations and functional implications

Schizophrenia is a chronic debilitating neuropsychiatric disorder with a complex genetic contribution. Although multiple genetic, immunological and environmental factors are known to contribute to schizophrenia susceptibility, the underlying neurobiological mechanism(s) is yet to be established. The immune system dysfunction theory of schizophrenia is experiencing a period of renewal due to a growth in evidence implicating components of the immune system in brain function and human behavior. Current evidence indicates that certain immune molecules such as Major Histocompatibility Complex (MHC) and cytokines, the key regulators of immunity and inflammation are directly involved in the neurobiological processes related to neurodevelopment, neuronal plasticity, learning, memory and behavior. However, the strongest support in favor of the immune hypothesis has recently emerged from on-going genome wide association studies advocating MHC region variants as major determinants of one's risk for developing schizophrenia. Further identification of the interacting partners and receptors of MHC molecules in the brain and their role in down-stream signaling pathways of neurotransmission have implicated these molecules as potential schizophrenia risk factors. More recently, combined brain imaging and genetic studies have revealed a relationship between genetic variations within the MHC region and neuromorphometric changes during schizophrenia. Furthermore, MHC molecules play a significant role in the immune-infective and neurodevelopmental pathogenetic pathways, currently hypothesized to contribute to the pathophysiology of schizophrenia. Herein, we review the immunological, genetic and expression studies assessing the role of the MHC in conferring risk for developing schizophrenia, we summarize and discuss the possible mechanisms involved, making note of the challenges to, and future directions of, immunogenetic research in schizophrenia.

Immunomodulation in schizophrenia: A study among the Indian schizophrenia patients of Siliguri, West Bengal

Authors investigated the circumstantial evidence for autoimmunity in schizophrenia patients of Siliguri by considering the immune parameters like HLA Class I genes, IL-2 and IL6 and T cell subsets. Low resolution PCR-SSP method was applied for typing the HLA genes. Serum levels of IL-2 and IL-6 were measured by ELISA method. The CD4+ and CD8+ subset count were done using flow cytometry. A significant increase in HLA A*03 gene was observed in patients along with the significant decrease of HLA-A*31 and HLA-B*51. Both IL-2 and IL-6 were found to have decreased levels in the patients. Although the mean percentage of CD4+ and CD8+ cells was higher in patients but not significantly higher than controls. These cumulative preliminary findings are suggestive of alterations in the immune system of schizophrenia patients of this region.

Monocytic HLA DR antigens in schizophrenic patients

A genetic association of specific human leukocyte antigens (HLA) DR genes and schizophrenia has recently been shown. These HLA play a fundamental role in the control of immune responses. Furthermore infectious agents have been proposed to be involved in the pathogenesis of schizophrenia. In this study we investigated the rate of HLA DR positive monocytes in schizophrenic patients compared to controls with a special focus on the adaption to in vitro stimulation with toll-like receptor ligands. Patients with schizophrenia and matched controls were included. For each individual, we evaluated the rate of HLA DR positive monocytes (either incubated at 37 °C or after stimulation with lipopolysaccharide or Poly I:C). We found a significantly higher percentage of schizophrenic patients with elevated HLA DR positive cells (p=0.045) as compared to controls. The adjustment rate from baseline levels of monocytic HLA DR positive cells to stimulation with Poly I:C was significantly lower in schizophrenic patients (p=0.038). The increased monocytic HLA DR in schizophrenic patients and the maladjustment of their monocytic HLA DR levels to an infectious stimulus might be a sign for a disturbed monocytic immune balance in schizophrenic individuals.

HLA-DRB1 association with schizophrenia in Saudi Arabian patients

OBJECTIVE

This study is aimed to examine the association between HLA-DRB1 alleles frequency and schizophrenia in Saudi Arabs.

METHODS

The DRB1 region of major histocompatibility complex was screened by polymerase chain reaction/sequence specific primers (PCR/SSP) in 180 schizophrenia patients and 200 matched controls.

RESULTS

The frequency of DRB1*03 was found to be significantly higher in schizophrenia patients as compared to controls, whereas a significantly lower frequency of DRB1*06 was observed in schizophrenia patients as compared to controls. Molecular sub-typing of the most prevalent allele DRB1*03 (30.56%) revealed the presence of DRB1*030101, *030102 alleles.

CONCLUSION

The results of this study suggested a positive association between DRB1*03 (DRB1*030101, DRB1*030102) with schizophrenia and a negative association of DRB1*06 with schizophrenia in Saudi Arabs. However it is not clear whether the DRB1*03 alleles have a direct causal role in the etiology of schizophrenia or if they are in direct linkage disequilibrium with another true susceptibility locus. Since schizophrenia is a complex phenotype, it is expected that many factors might act together to produce the final outcome. Further studies are warranted involving larger population to confirm the observations reported in this study.

Association study of HLA-A gene and schizophrenia in Han Chinese from Taiwan

Dysregulation of the immune response has been proposed as a precipitating factor of schizophrenia, and human leukocyte antigens (HLA) play a critical role in regulating the cascade of immunological reaction. Hence, many studies have investigated the relationship between the HLA system and schizophrenia. HLA is a complex gene family that contains several highly polymorphic genes, while the HLA-A gene is the most often studied gene to be associated with schizophrenia in the literature. A recent study reported that the interaction of the HLA-A10 allele and Chlamydial infection was highly associated with schizophrenia in a German population, which prompted us to investigate whether the HLA-A gene was also associated with schizophrenia in our population. Using a sequencing-based HLA typing method, we determined the HLA-A genotypes in 377 Han Chinese patients with schizophrenia (214 males, 163 females) and 321 non-psychotic Han Chinese control subjects (164 males, 157 females) from Taiwan. In total, 26 DNA-defined HLA-A alleles were identified in this sample. However, no significant differences of these allelic frequencies were found between the patients and the control subjects, suggesting that the HLA-A gene was unlikely a major risk factor of schizophrenia in this sample. As different populations have different HLA polymorphisms, an examination of the relationship of other HLA genes and schizophrenia in our population, with a larger sample size, is warranted in the future.

Seasonal birth patterns in myositis subgroups suggest an etiologic role of early environmental exposures

OBJECTIVE

To evaluate whether seasonal early environmental exposures might influence later development of autoimmune disease, by assessing distributions of birth dates in groups of patients with idiopathic inflammatory myopathies (IIMs).

METHODS

We assessed birth patterns in groups of patients with juvenile-onset IIM (n = 307) and controls (n = 3,942) who were born between 1970 and 1999, and in groups of patients with adult-onset IIM (n = 668) and controls (n = 6,991) who were born between 1903 and 1982. Birth dates were analyzed as circular data. Seasonal clustering was assessed by the Rayleigh test, and differences between groups by a rank-based uniform scores test.

RESULTS

The overall birth distributions among patients with juvenile IIM and among patients with adult IIM did not differ significantly from those among juvenile and adult controls, respectively. Some subgroups of patients with juvenile IIM had seasonal birth distributions. Hispanic patients with juvenile-onset IIM had a seasonal birth pattern (mean birth date October 16) significantly different from that of Hispanic controls (P = 0.002), who had a uniform birth distribution, and from that of non-Hispanic patients with juvenile-onset IIM (P < 0.001), who had a mean birth date of May 2. Juvenile dermatomyositis patients with p155 autoantibody had a birth distribution that differed significantly from that of p155 antibody-negative juvenile dermatomyositis patients (P = 0.003). Juvenile IIM patients with the HLA risk factor allele DRB1*0301 had a birth distribution significantly different from those without the allele (P = 0.021). Similar results were observed for juvenile and adult IIM patients with the linked allele DQA1*0501, versus juvenile and adult IIM patients without DQA1*0501, respectively. No significant patterns in birth season were found in other subgroups.

CONCLUSION

Birth distributions appear to have stronger seasonality in juvenile than in adult IIM subgroups, suggesting greater influence of perinatal exposures on childhood-onset illness. Seasonal early-life exposures may influence the onset of some autoimmune diseases later in life.

Genetic associations between delusional disorder and paranoid schizophrenia: A novel etiologic approach

OBJECTIVES

Genetic associations between delusional disorder and paranoid schizophrenia are not well understood, although involvement of biological factors has been suspected. We investigated the incidence of human leukocyte antigen (HLA) class I alleles in patients with delusional disorder and paranoid schizophrenia, first, to explore a possible immunogenetic etiology of these paranoid disorders and, second, to determine whether they share similar etiologic mechanisms.

METHOD

We employed a nested case-control study design. Psychiatric reference data were available for 38,500 patients attending a hospital-based psychiatric outpatient department between 1998 and 2005. We enrolled 100 patients with delusional disorder and 50 patients with paranoid schizophrenia as the subject cases, using DSM-IV criteria. We considered equivalent numbers of healthy volunteers matched for age and ethnic background as control subjects. All subjects came from an India-born Bengali population. We applied the polymerase chain reaction-based molecular typing method to all patients and healthy subjects.

RESULTS

The HLA-A*03 gene is significantly associated with delusional disorder as well as with paranoid schizophrenia. This HLA gene alone or in linkage disequilibrium with other HLA genes or other closely linked non-HLA genes may influence susceptibility to delusional disorder and paranoid schizophrenia.

CONCLUSIONS

The study reveals important associations between HLA genes and paranoid disorders. Delusional disorder and paranoid schizophrenia may share similar etiologic mechanisms. This preliminary observation may help our understanding of the genetic basis of these paranoid disorders.

Human leukocyte antigen DR1 in Japanese and Turkish patients with schizophrenia

The main focus of this review has been to discuss the probable causes of the higher frequency of HLA DR1 antigen in patients with schizophrenia from Japan and Turkey, and also to see whether there was an impact of belonging to the Ural-Altaic language group. A general medline search on the terms HLA and schizophrenia was used as the method to determine HLA studies in patients with schizophrenia. Most of the findings were inconsistent regarding the increased or decreased frequencies of different Class I and II antigens. However, there were interesting results, which have been consistently repeated in several Japanese studies and in a Turkish study. HLA DR1 antigen was statistically significantly increased in Japanese and Turkish patients with schizophrenia. As Japanese and Turkish languages belong to the Ural-Altaic language group, HLA DR1 antigen might have a specific association with schizophrenia in Japanese and Turkish patients. Searching the frequency of HLA DR1 antigen in patients with schizophrenia in other members of Ural-Altaic language group is necessary to support this hypothesis. Other language groups (e.g. Indo-European) should be assessed as well.

Seasonality of schizophrenia births in the Japanese population: increased winter births possibly confined to the north area

A number of North American and European studies have observed a higher proportion of winter births in schizophrenia patients. Thus, seasonal fluctuation of unknown environmental factors may affect brain development in ways that alter susceptibility to schizophrenia. Specification of these factors may help elucidate the etiopathological mechanism of the disease, about which little is certain. A small number of studies have investigated this issue in Asian populations, and the findings are not as consistent as those of Western populations. No remarkable excess of winter births has been observed in Japanese or Korean studies, while some studies have reported a significant decrease of summer births. We further investigated the issue in Japanese patients with schizophrenia (n=3927). No significant excess of winter births was observed, but a decrease in the summer births was found in male subjects. This is largely consistent with previous Japanese studies; however, when the subjects were confined to those born in a colder and higher latitude area of Japan (n=1338), a consistent trend for both a winter increase, and a summer decrease, was found. However, the results did not consistently reach statistical significance, possibly due to the lack of statistical power. Environmental factors that correlate with latitude might play a role in the development of the seasonality of births in schizophrenia. Further studies in a larger sample size are required to test these possibilities.

Maternal exposure to first-trimester sunshine is associated with increased birth weight in human infants

Two alternative hypotheses have been generated to account for seasonal variation in the birth weight of human infants born in industrialized countries. First, it has been hypothesized that low ambient temperature during the second trimester of gestation decreases birth weight. Second, it has been hypothesized that exposure to bright sunshine during the first trimester increases birth weight. We tested these two hypotheses to determine which, if either, accounted for seasonal variation in birth weight of full-term infants. Birth weight data, collected over a 5-year period, were analyzed as a function of peak and trough sunshine and ambient temperature. Although there was no effect of ambient temperature during any trimester on birth weight, infants whose mothers were exposed to peak sunshine during their first trimester were born significantly heavier than infants whose mothers experienced trough levels of sunshine during the same trimester. Furthermore, infants whose mothers were exposed to trough levels of sunshine during their second and third trimesters were born significantly heavier than infants whose mothers were exposed to peak levels of sunshine during the same trimesters. We hypothesize that high levels of sunshine during early gestation may increase the level of insulin-like growth factor (IGF)-1, facilitating prenatal growth.

A study of HLA-linked genes in a monosymptomatic psychotic disorder in an Indian Bengali population

OBJECTIVE

The etiology of delusional disorder is imperfectly understood. Involvement of biological factors has long been suspected. We examined the incidence of class I human leukocyte antigens (HLAs) in patients with delusional disorder to understand the role of HLA genes and explore a possible immunogenetic etiology for delusional disorder.

METHODS

We used a nested case-control study design. Psychiatric reference data were available for 27 500 patients registered between 1998 and 2003. Initially, we enrolled 150 patients with delusional disorder from the India-born Bengali population, using DSM-IV diagnostic criteria. After longitudinal follow-up, 80 patients were found to have only delusional disorder, while the remaining 70 patients represented different illnesses with paranoid symptoms and were excluded. We performed serological typing on all 150 patients and applied the polymerase chain reaction-based high-resolution molecular typing method to the 80 patients with delusional disorder. Eighty healthy donors of the same ethnic background, matched for age, sex, and other socioeconomic variables, formed the control group.

RESULTS

Some of the HLA alleles were associated with delusional disorder, and the gene HLA-A*03 was found to be significantly more frequent. This gene may influence patients' susceptibility to delusional disorder.

CONCLUSION

The study reveals important associations between HLA genes and delusional disorder. This preliminary observation may help our understanding of this disorder's genetic basis.

Is the season of birth association with psychosis due to seasonal variations in foetal growth or other related exposures? A cohort study

OBJECTIVE

To investigate the association between season of birth and psychosis, and to assess whether any association is caused by seasonal fluctuations in foetal growth or other related exposures.

METHOD

Cohort of 747 432 Swedish males and females born between 1973 and 1980 and followed up from 16 years of age to 31 December 1999. Psychiatric admissions were identified using the Swedish Inpatient Discharge Register. The analysis is based on the 696 025 subjects with complete data.

RESULTS

A total of 506 (0.07%) subjects developed schizophrenia and 879 (0.13%) non-affective non-schizophrenic psychoses. There was a moderate increased risk of schizophrenia amongst winter births, hazard ratio 1.23 (95% confidence interval 0.96-1.59), but this did not reach conventional levels of statistical significance. There was no association with non-affective psychoses. We found no evidence that associations were confounded by measures of foetal growth or maternal socioeconomic position. There was no evidence that seasonal effects on schizophrenia differed in men and women.

CONCLUSION

Season of birth associations with schizophrenia do not appear to be confounded by birth-related exposures.

Gene-environment interaction in psychiatric disorders as indicated by season of birth variations in tryptophan hydroxylase (TPH), serotonin transporter (5-HTTLPR) and dopamine receptor (DRD4) gene polymorphisms

Genetic and environmental factors, as well as their interactions, are likely to be involved in psychiatric disorders. Considerable progress has been made in association and linkage studies with various candidate genes, at times with conflicting or ambiguous results. An environmental factor that has persistently shown associations with several psychiatric and neurological disorders is the season of birth. If it is the interaction of a specific gene allele with a specific season of birth that constitutes an increased (or decreased) risk for a disorder, then the individuals with this disorder are likely to have a season of birth variation in this gene allele. We investigated the variations in TPH, 5-HTTLPR and DRD4 gene polymorphisms according to seasonality of birth in 954 patients with unipolar affective disorder, bipolar affective disorder, and schizophrenia, respectively, and in 395 controls. We first analyzed season of birth variations in the gene alleles with one cycle or two cycles per year, and then compared specified birth seasons with each other. We found season of birth variations in these gene alleles that were different for different psychiatric disorders. Significant differences between cases and controls could be obtained when restricting the analysis within certain birth seasons but not within others. Our results thus suggest an interaction between the seasons of birth and the expression of the candidate genes, and that season of birth is a confounding variable when investigating the role of the candidate genes in susceptibility to psychiatric disorders.

Genetically mediated brain abnormalities in schizophrenia

Schizophrenia is a highly heritable, neurobehavioral disorder; however, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Some consistent linkage findings have emerged on chromosomes 1, 6, 8, 11, 13, 15, and 22. New methods are being developed for candidate gene identification, including the use of neurobiologic phenotypes observed in relatives of persons with schizophrenia. Neuroimaging studies of relatives implicate abnormal hippocampal structure and inefficient prefrontal network functioning, probably representing mild variants of the abnormalities observed in schizophrenia. These characteristics may represent stable markers of vulnerability to schizophrenia, because they are not confounded by effects of antipsychotic drugs or psychosis. Recent studies provide evidence for a small role of the catechol-O-methyltransferase gene on 22q, and the serotonin receptor transporter gene on 17q11-q12 in the development of schizophrenia. Linking genes and brain regions or networks is an important step in identification of the pathophysiology of schizophrenia.

Human leukocyte antigen-A specificities and its relation with season of birth in Japanese patients with schizophrenia

Several studies, including one from Japan, have observed an increase of Human Leukocyte Antigen (HLA)-A24 and A26 in schizophrenia, although others failed to observe the increase. No use of systematic diagnostic criteria and a not-adequately reliable typing technique might have affected the results in the previous studies. We investigated HLA-A specificities in Japanese patients with schizophrenia (DSM-IV), recruited from the same area as in the early Japanese study. A DNA-based technique (polymerase chain reaction-microtiter plate hybridization) was employed. No significant difference was observed in frequencies of any HLA-A specificities between patients and controls, including A24 and A26. No significant association was found between the HLA-A and birth-season in patients. Thus, no evidence was obtained for an association between HLA-A and schizophrenia from the Japanese population.

Molecular genetic studies of schizophrenia: challenges and insights

Schizophrenia (SCZ) is a mental disease that affects approximately 1% of the population with life-long devastating consequences. Based on evidence for a major contribution of genetic factors, a decade of extensive efforts has been dedicated to the search of DNA sequence variations that increase the risk to SCZ. Search for genes in rare multiplex SCZ families with a large number of affected individuals and quasi-Mendelian mode of inheritance using genetic linkage methodology has been one of the favorite strategies in psychiatric genetics. Although several genomic regions were suggested for linkage to SCZ, not a single gene causing or predisposing to SCZ has been identified thus far. Furthermore, it is not clear whether the genes of familial SCZ are also involved in sporadic cases that represent the overwhelming majority of SCZ patients. For sporadic cases, genetic association studies comparing the distribution of allelic frequencies of candidate genes in SCZ patients and controls have been performed but the outcome of such studies has also been quite modest. Several factors such as possible involvement of numerous interactive genes of minor effect, yet unknown environmental effects and diagnostic ambiguities of the disease have made genetic studies in SCZ quite unproductive. In terms of future studies, a genome-wide association search is a promising approach; however, this approach requires genotyping of thousands of genetic markers in large samples. In addition, a detailed analysis of the genes, expression of which changes under the influence of environmental factors, can indicate good candidates for genetic association studies. In this connection, investigations of the epigenetic regulation of genes and not only the DNA sequence variation, may be necessary for complete understanding of the etiopathogenic mechanisms of SCZ.

Season of birth in Japanese patients with schizophrenia

A number of North American and European studies have observed a higher proportion of winter births in schizophrenia patients. Fewer studies have investigated this issue in Asian populations, and the findings are not as consistent as in the studies of Western populations. A statistically significant excess of winter births has not been observed in Japanese or Korean studies, while some of the studies found a decreased number of summer births among their patients. We further investigated the issue in Japanese patients with schizophrenia (n=2985). No significant excess of winter births was observed. Spearman correlation between schizophrenia births and ambient temperature was not significant. However, a decrease in the summer births was found, consistent with most of the previous Japanese studies. When analyzed by gender, a decrease in summer births was found in males, but not in females. In addition, a trend towards an increase in winter births was observed and Spearman correlation between low ambient temperature and schizophrenia births was significant in male subjects. More significant seasonality of birth in male patients than in female patients might be related to more susceptibility to pre- or perinatal disturbances in neurodevelopment in males than in females.