Lack of Support for the Genes by Early Environment Interaction Hypothesis in the Pathogenesis of Schizophrenia

A Genome-Wide Association Study of First-Episode Psychosis: A Genetic Exploration in an Italian Cohort

BACKGROUND

Psychosis, particularly schizophrenia (SZ), is influenced by genetic and environmental factors. The neurodevelopmental hypothesis suggests that genetic factors affect neuronal circuit connectivity during perinatal periods, hence causing the onset of the diseases. In this study, we performed a genome-wide association study (GWAS) in a sample of the first episode of psychosis (FEP).

METHODS

A sample of 147 individuals diagnosed with non-affective psychosis and 102 controls were recruited and assessed. After venous blood and DNA extraction, the samples were genotyped. Genetic data underwent quality controls, genotype imputation, and a case-control genome-wide association study (GWAS). After the GWAS, results were investigated using an in silico functional mapping and annotation approach.

RESULTS

Our GWAS showed the association of 27 variants across 13 chromosomes at genome-wide significance (p < 1 × 10-7) and a total of 1976 candidate variants across 188 genes at suggestive significance (p < 1 × 10-5), mostly mapping in non-coding or intergenic regions. Gene-based tests reported the association of the SUFU (p = 4.8 × 10-7) and NCAN (p = 1.6 × 10-5) genes. Gene-sets enrichment analyses showed associations in the early stages of life, spanning from 12 to 24 post-conception weeks (p < 1.4 × 10-3) and in the late prenatal period (p = 1.4 × 10-3), in favor of the neurodevelopmental hypothesis. Moreover, several matches with the GWAS Catalog reported associations with strictly related traits, such as SZ, as well as with autism spectrum disorder, which shares some genetic overlap, and risk factors, such as neuroticism and alcohol dependence.

CONCLUSIONS

The resulting genetic associations and the consequent functional analysis displayed common genetic liability between the non-affective psychosis, related traits, and risk factors. In sum, our investigation provided novel hints supporting the neurodevelopmental hypothesis in SZ and-in general-in non-affective psychoses.

Demographic, Premorbid, and Clinical Characteristics of Schizophrenia Spectrum Patients with High and Low Polygenic Liability to the Disorder

BACKGROUND/OBJECTIVES

Schizophrenia is a clinically heterogeneous complex disorder with a substantial polygenic basis. The discovery of phenotypes indexing genetic differences advances research into the schizophrenia etiology but has proven to be challenging. The study aimed to further clarify the relationships of schizophrenia polygenic risk scores (SZ-PRSs) with a comprehensive array of schizophrenia antecedents and presentations using a culturally and ethnically homogeneous sample of schizophrenia spectrum patients.

METHODS

The top and bottom deciles (n = 172) of the SZ-PRS distribution in a group of 861 patients were compared on information derived from medical records using logistic regression.

RESULTS

High SZ-PRSs were associated with female sex, family history of a wide range of neuropsychiatric conditions, moderately poor premorbid social and cognitive adjustment in childhood, the schizophrenia diagnosis, and positive and "abnormal" psychomotor symptoms. The low-SZ-PRS group demonstrated an accumulation of both individuals with milder forms of SZ spectrum disorders and those with severe premorbid abnormalities in the social, cognitive, and neurological domains.

CONCLUSIONS

The results highlight moderately poor premorbid social and cognitive adjustment as characteristic manifestations of the polygenic component of the schizophrenia etiology and provide the first piece of PRS-based evidence for the long-standing idea of a higher liability threshold in women. The presence of milder and severe cases in the bottom SZ-PRS decile, suggesting its etiological heterogeneity, might be an important source of the inconsistency in the previous research on SZ-PRSs' relationship with schizophrenia phenotypes and should be considered in future studies.

Polygenic and Polyenvironment Interplay in Schizophrenia-Spectrum Disorder and Affective Psychosis; the EUGEI First Episode Study

BACKGROUND

Multiple genetic and environmental risk factors play a role in the development of both schizophrenia-spectrum disorders and affective psychoses. How they act in combination is yet to be clarified.

METHODS

We analyzed 573 first episode psychosis cases and 1005 controls, of European ancestry. Firstly, we tested whether the association of polygenic risk scores for schizophrenia, bipolar disorder, and depression (PRS-SZ, PRS-BD, and PRS-D) with schizophrenia-spectrum disorder and affective psychosis differed when participants were stratified by exposure to specific environmental factors. Secondly, regression models including each PRS and polyenvironmental measures, including migration, paternal age, childhood adversity and frequent cannabis use, were run to test potential polygenic by polyenvironment interactions.

RESULTS

In schizophrenia-spectrum disorder vs controls comparison, PRS-SZ was the strongest genetic predictor, having a nominally larger effect in nonexposed to strong environmental factors such as frequent cannabis use (unexposed vs exposed OR 2.43 and 1.35, respectively) and childhood adversity (3.04 vs 1.74). In affective psychosis vs controls, the relative contribution of PRS-D appeared to be stronger in those exposed to environmental risk. No evidence of interaction was found between any PRS with polyenvironmental score.

CONCLUSIONS

Our study supports an independent role of genetic liability and polyenvironmental risk for psychosis, consistent with the liability threshold model. Whereas schizophrenia-spectrum disorders seem to be mostly associated with polygenic risk for schizophrenia, having an additive effect with well-replicated environmental factors, affective psychosis seems to be a product of cumulative environmental insults alongside a higher genetic liability for affective disorders.

Exploring the causal effect of placental physiology in susceptibility to mental and addictive disorders: a Mendelian randomization study

Background

Epidemiological studies have linked low birth weight to psychiatric disorders, including substance use disorders. Genomic analyses suggest a role of placental physiology on psychiatric risk. We investigated whether this association is causally related to impaired trophoblast function.

Methods

We conducted a two-sample summary-data Mendelian randomization study using as instrumental variables those genetic variants strongly associated with birth weight, whose effect is exerted through the fetal genome, and are located near genes with differential expression in trophoblasts. Eight psychiatric and substance use disorders with >10,000 samples were included as outcomes. The inverse variance weighted method was used as the main analysis and several sensitivity analyses were performed for those significant results.

Results

The inverse variance weighted estimate, based on 14 instrumental variables, revealed an association, after correction for multiple tests, between birth weight and broadly defined depression (β = -0.165, 95% CI = -0.282 to -0.047, P = 0.0059). Sensitivity analyses revealed the absence of heterogeneity in the effect of instrumental variables, confirmed by leave-one-out analysis, MR_Egger intercept, and MR_PRESSO. The effect was consistent using robust methods. Reverse causality was not detected. The effect was specifically linked to genetic variants near genes involved in trophoblast physiology instead of genes with fetal effect on birth weight or involved in placenta development.

Conclusion

Impaired trophoblast functioning, probably leading to reduced fetal brain oxygen and nutrient supply, is causally related to broadly defined depression. Considering the therapeutic potential of some agents to treat fetal growth restriction, further research on the effect of trophoblast physiology on mental disorders may have future implications in prevention.

The interaction between early life complications and a polygenic risk score for schizophrenia is associated with brain activity during emotion processing in healthy participants

BACKGROUND

Previous evidence suggests that early life complications (ELCs) interact with polygenic risk for schizophrenia (SCZ) in increasing risk for the disease. However, no studies have investigated this interaction on neurobiological phenotypes. Among those, anomalous emotion-related brain activity has been reported in SCZ, even if evidence of its link with SCZ-related genetic risk is not solid. Indeed, it is possible this relationship is influenced by non-genetic risk factors. Thus, this study investigated the interaction between SCZ-related polygenic risk and ELCs on emotion-related brain activity.

METHODS

169 healthy participants (HP) in a discovery and 113 HP in a replication sample underwent functional magnetic resonance imaging (fMRI) during emotion processing, were categorized for history of ELCs and genome-wide genotyped. Polygenic risk scores (PRSs) were computed using SCZ-associated variants considering the most recent genome-wide association study. Furthermore, 75 patients with SCZ also underwent fMRI during emotion processing to verify consistency of their brain activity patterns with those associated with risk factors for SCZ in HP.

RESULTS

Results in the discovery and replication samples indicated no effect of PRSs, but an interaction between PRS and ELCs in left ventrolateral prefrontal cortex (VLPFC), where the greater the activity, the greater PRS only in presence of ELCs. Moreover, SCZ had greater VLPFC response than HP.

CONCLUSIONS

These results suggest that emotion-related VLPFC response lies in the path from genetic and non-genetic risk factors to the clinical presentation of SCZ, and may implicate an updated concept of intermediate phenotype considering early non-genetic factors of risk for SCZ.

Difficulties during delivery, brain ventricle enlargement and cognitive impairment in first episode psychosis

BACKGROUND

Patients with a first episode of psychosis (FEP) display clinical, cognitive, and structural brain abnormalities at illness onset. Ventricular enlargement has been identified in schizophrenia since the initial development of neuroimaging techniques. Obstetric abnormalities have been associated with an increased risk of developing psychosis but also with cognitive impairment and brain structure abnormalities. Difficulties during delivery are associated with a higher risk of birth asphyxia leading to brain structural abnormalities, such as ventriculomegaly, which has been related to cognitive disturbances.

METHODS

We examined differences in ventricular size between 142 FEP patients and 123 healthy control participants using magnetic resonance imaging. Obstetric complications were evaluated using the Lewis-Murray scale. We examined the impact of obstetric difficulties during delivery on ventricle size as well as the possible relationship between ventricle size and cognitive impairment in both groups.

RESULTS

FEP patients displayed significantly larger third ventricle size compared with healthy controls. Third ventricle enlargement was associated with diagnosis (higher volume in patients), with difficulties during delivery (higher volume in subjects with difficulties), and was highest in patients with difficulties during delivery. Verbal memory was significantly associated with third ventricle to brain ratio.

CONCLUSIONS

Our results suggest that difficulties during delivery might be significant contributors to the ventricular enlargement historically described in schizophrenia. Thus, obstetric complications may contribute to the development of psychosis through changes in brain architecture.

Stress, Environment and Early Psychosis

Existing literature provides extended evidence of the close relationship between stress dysregulation, environmental insults, and psychosis onset. Early stress can sensitize genetically vulnerable individuals to future stress, modifying their risk for developing psychotic phenomena. Neurobiological substrate of the aberrant stress response to hypothalamic-pituitary-adrenal axis dysregulation, disrupted inflammation processes, oxidative stress increase, gut dysbiosis, and altered brain signaling, provides mechanistic links between environmental risk factors and the development of psychotic symptoms. Early-life and later-life exposures may act directly, accumulatively, and repeatedly during critical neurodevelopmental time windows. Environmental hazards, such as pre- and perinatal complications, traumatic experiences, psychosocial stressors, and cannabis use might negatively intervene with brain developmental trajectories and disturb the balance of important stress systems, which act together with recent life events to push the individual over the threshold for the manifestation of psychosis. The current review presents the dynamic and complex relationship between stress, environment, and psychosis onset, attempting to provide an insight into potentially modifiable factors, enhancing resilience and possibly influencing individual psychosis liability.

High-throughput screening of glucocorticoid-induced enhancer activity reveals mechanisms of stress-related psychiatric disorders

Exposure to stressful life events increases the risk for psychiatric disorders. Mechanistic insight into the genetic factors moderating the impact of stress can increase our understanding of disease processes. Here, we test 3,662 single nucleotide polymorphisms (SNPs) from preselected expression quantitative trait loci in massively parallel reporter assays to identify genetic variants that modulate the activity of regulatory elements sensitive to glucocorticoids, important mediators of the stress response. Of the tested SNP sequences, 547 were located in glucocorticoid-responsive regulatory elements of which 233 showed allele-dependent activity. Transcripts regulated by these functional variants were enriched for those differentially expressed in psychiatric disorders in the postmortem brain. Phenome-wide Mendelian randomization analysis in 4,439 phenotypes revealed potentially causal associations specifically in neurobehavioral traits, including major depression and other psychiatric disorders. Finally, a functional gene score derived from these variants was significantly associated with differences in the physiological stress response, suggesting that these variants may alter disease risk by moderating the individual set point of the stress response.

The impact of placental genomic risk for schizophrenia and birth asphyxia on brain development

The placenta plays a role in fetal brain development, and pregnancy and birth complications can be signs of placental dysfunction. Birth asphyxia is associated with smaller head size and higher risk of developing schizophrenia (SZ), but whether birth asphyxia and placental genomic risk factors associated with SZ are related and how they might impact brain development is unclear. 433 adult patients with SZ and 870 healthy controls were clinically evaluated and underwent brain magnetic resonance imaging. Pregnancy and birth information were obtained from the Medical Birth Registry of Norway. Polygenic risk scores (PRS) from the latest genome-wide association study in SZ were differentiated into placental PRS (PlacPRS) and non-placental PRS. If the interaction between PRSs and birth asphyxia on case-control status was significant, neonatal head circumference (nHC) and adult intracranial volume (ICV) were further evaluated with these variables using multiple regression. PlacPRS in individuals with a history of birth asphyxia was associated with a higher likelihood of being a patient with SZ (t = 2.10, p = 0.018). We found a significant interaction between PlacPRS and birth asphyxia on nHC in the whole sample (t = -2.43, p = 0.008), with higher placental PRS for SZ associated with lower nHC in those with birth asphyxia. This relationship was specific to males (t = -2.71, p = 0.005) and also found with their adult ICV (t = -1.97, p = 0.028). These findings suggest that placental pathophysiology and birth asphyxia may affect early and late trajectories of brain development, particularly in males with a higher vulnerability to SZ. This knowledge might lead to new strategies of treatment and prevention in SZ.

Effect of polygenic risk score, family load of schizophrenia and exposome risk score, and their interactions, on the long-term outcome of first-episode psychosis

BACKGROUND

Consistent evidence supports the involvement of genetic and environmental factors, and their interactions, in the etiology of psychosis. First-episode psychosis (FEP) comprises a group of disorders that show great clinical and long-term outcome heterogeneity, and the extent to which genetic, familial and environmental factors account for predicting the long-term outcome in FEP patients remains scarcely known.

METHODS

The SEGPEPs is an inception cohort study of 243 first-admission patients with FEP who were followed-up for a mean of 20.9 years. FEP patients were thoroughly evaluated by standardized instruments, with 164 patients providing DNA. Aggregate scores estimated in large populations for polygenic risk score (PRS-Sz), exposome risk score (ERS-Sz) and familial load score for schizophrenia (FLS-Sz) were ascertained. Long-term functioning was assessed by means of the Social and Occupational Functioning Assessment Scale (SOFAS). The relative excess risk due to interaction (RERI) was used as a standard method to estimate the effect of interaction of risk factors.

RESULTS

Our results showed that a high FLS-Sz gave greater explanatory capacity for long-term outcome, followed by the ERS-Sz and then the PRS-Sz. The PRS-Sz did not discriminate significantly between recovered and non-recovered FEP patients in the long term. No significant interaction between the PRS-Sz, ERS-Sz or FLS-Sz regarding the long-term functioning of FEP patients was found.

CONCLUSIONS

Our results support an additive model of familial antecedents of schizophrenia, environmental risk factors and polygenic risk factors as contributors to a poor long-term functional outcome for FEP patients.

Associations between the urban environment and psychotic experiences in adolescents

OBJECTIVE

In 2050 two-thirds of the world's population is predicted to live in cities, which asks for a better understanding of how the urban environment affects mental health. Urbanicity has repeatedly been found to be a risk factor, in particular for psychosis. Here, we explored what factors of the urban exposome underlie the association between urban characteristics and psychotic experiences (PE) in adolescents.

METHODS

Participants were 815 adolescents (mean age 14.84 years, SD 0.78) from an at-risk cohort (greater Rotterdam area, the Netherlands) oversampled on their self-reported emotional and behavioral problems. We used linear regression analysis to examine the association with detailed geodata on urbanicity (surrounding address density), green space density (high and low vegetation), and mixed noise levels (road, rail, air, industry, and wind power) with PE in adolescents. Analyses were adjusted for multiple socio-economic and parental confounders. Furthermore, we explored sex-interaction effects.

RESULTS

Higher surrounding address density and low greenspace density were each independently associated with more PE (B = 0.18, 95 % CI 0.02; 0.34 and B = 0.17, 95 % CI 0.01; 0.32, respectively). High mixed noise levels were only associated with more PE in boys (B = 0.23, 95 % CI 0.01; 0.46). A sex-interaction effect was found for high urbanicity (B = -0.46, 95 % CI -0.77; -0.14) and low greenspace density (B = -0.49, 95 % CI -0.73; -0.11), illustrating that these associations with PE were specific for boys.

CONCLUSION

Multiple characteristics of living in an urban area are associated with more PE in adolescent boys. Our observations provide leads for prevention of mental health problems via urban designing.

Obstetric complications and genetic risk for schizophrenia: Differential role of antenatal and perinatal events in first episode psychosis

BACKGROUND

Obstetric complications (OCs) are key contributors to psychosis risk. However, it is unclear whether they increase psychosis vulnerability independently of genetic risk, in interaction with it, or are a manifestation of psychosis proneness. We examined the role of distinct types of OCs in terms of psychosis risk and tested whether they interact differently with genetic vulnerability, whilst accounting for other known environmental risk factors.

STUDY DESIGN

405 participants (219 first episode psychosis patients and 186 healthy volunteers) underwent a comprehensive assessment of OCs, measured using the Lewis-Murray scale and divided into complications of pregnancy, abnormalities of foetal growth and development, and complications of delivery. Participants were compared in terms of history of OCs, polygenic risk score for schizophrenia (PRS-SZ) and interactions between these.

RESULTS

Both complications of pregnancy and abnormalities of foetal growth were significantly associated with case-control status (p = 0.02 and 0.03, respectively), whereas complications of delivery were not. PRS-SZ showed a significant association with psychosis (p = 0.04), but there were no significant interactions between genetic risk for schizophrenia and OCs, either when these were considered globally or separated based on their timeframe.

CONCLUSIONS

We observed no significant interaction between genetic and obstetric vulnerability, yet distinct types of OCs may have a different impact on psychosis risk, based on their nature and timeframe. Examining their differential role might clarify their relative contributions to this risk.

Prioritization of potential causative genes for schizophrenia in placenta

Our earlier work has shown that genomic risk for schizophrenia converges with early life complications in affecting risk for the disorder and sex-biased neurodevelopmental trajectories. Here, we identify specific genes and potential mechanisms that, in placenta, may mediate such outcomes. We performed TWAS in healthy term placentae (N = 147) to derive candidate placental causal genes that we confirmed with SMR; to search for placenta and schizophrenia-specific associations, we performed an analogous analysis in fetal brain (N = 166) and additional placenta TWAS for other disorders/traits. The analyses in the whole sample and stratifying by sex ultimately highlight 139 placenta and schizophrenia-specific risk genes, many being sex-biased; the candidate molecular mechanisms converge on the nutrient-sensing capabilities of placenta and trophoblast invasiveness. These genes also implicate the Coronavirus-pathogenesis pathway and showed increased expression in placentae from a small sample of SARS-CoV-2-positive pregnancies. Investigating placental risk genes for schizophrenia and candidate mechanisms may lead to opportunities for prevention that would not be suggested by study of the brain alone.

Study protocol of the Berlin Research Initiative for Diagnostics, Genetics and Environmental Factors in Schizophrenia (BRIDGE-S)

BACKGROUND

Large-scale collaborative efforts in the field of psychiatric genetics have made substantial progress in unraveling the biological architecture of schizophrenia (SCZ). Although both genetic and environmental factors are known to play a role in schizophrenia etiology our mechanistic understanding of how they shape risk, resilience and disease trajectories remains limited.

METHODS

Here, we present the study protocol of the Berlin Research Initiative for Diagnostics, Genetic and Environmental Factors of Schizophrenia (BRIDGE-S), which aims to collect a densely phenotyped genetic cohort of 1,000 schizophrenia cases and 1,000 controls. The study's main objectives are to build a resource for i) promoting genetic discoveries and ii) genotype-phenotype associations to infer specific disease subtypes, and iii) exploring gene-environment interactions using polyrisk models. All subjects provide a biological sample for genotyping and complete a core questionnaire capturing a variety of environmental exposures, demographic, psychological and health data. Approximately 50% of individuals in the sample will further undergo a comprehensive clinical and neurocognitive assessment.

DISCUSSION

With BRIDGE-S we created a valuable database to study genomic and environmental contributions to schizophrenia risk, onset, and outcomes. Results of the BRIDGE-S study could yield insights into the etiological mechanisms of schizophrenia that could ultimately inform risk prediction, and early intervention and treatment strategies.

Infections During Pregnancy and Risks for Adult Psychosis: Findings from the New England Family Study

For the past 40 years, our team has conducted a unique program of research investigating the prenatal risks for schizophrenia and related adult psychiatric disorders. The New England Family Study is a long-term prospective cohort study of over 16,000 individuals followed from the prenatal period for over 50 years. This chapter summarizes several major phases and findings from this work, highlighting recent results on maternal prenatal bacterial infections and brain imaging. Implications regarding the causes and potential prevention of major psychotic disorders are discussed.

Polygenic association with severity and long-term outcome in eating disorder cases

About 20% of individuals with anorexia nervosa (AN) remain chronically ill. Therefore, early identification of poor outcome could improve care. Genetic research has identified regions of the genome associated with AN. Patients with anorexia nervosa were identified via the Swedish eating disorder quality registers Stepwise and Riksät and invited to participate in the Anorexia Nervosa Genetics Initiative. First, we associated genetic information longitudinally with eating disorder severity indexed by scores on the Clinical Impairment Assessment (CIA) in 2843 patients with lifetime AN with or without diagnostic migration to other forms of eating disorders followed for up to 16 years (mean = 5.3 years). Second, we indexed the development of a severe and enduring eating disorder (SEED) by a high CIA score plus a follow-up time ≥5 years. We associated individual polygenic scores (PGSs) indexing polygenic liability for AN, schizophrenia, and body mass index (BMI) with severity and SEED. After multiple testing correction, only the BMI PGS when calculated with traditional clumping and p value thresholding was robustly associated with disorder severity (β_PGS = 1.30; 95% CI: 0.72, 1.88; p = 1.2 × 10^-5) across all p value thresholds at which we generated the PGS. However, using the alternative PGS calculation method PRS-CS yielded inconsistent results for all PGS. The positive association stands in contrast to the negative genetic correlation between BMI and AN. Larger discovery GWASs to calculate PGS will increase power, and it is essential to increase sample sizes of the AN GWASs to generate clinically meaningful PGS as adjunct risk prediction variables. Nevertheless, this study provides the first evidence of potential clinical utility of PGSs for eating disorders.

Obstetric Complications and Polygenic Risk Score: Which Role in Predicting a Severe Short-Term Outcome in Psychosis?

Understanding and improving the outcomes of psychosis remains a major challenge for clinical research. Obstetric complications (OCs) as a risk factor for schizophrenia (SZ) have been investigated as a potential predictor of outcomes in relation to illness severity and poorer treatment outcome, but there are less reports on first episode psychosis (FEP) patients. We test whether OCs, collected in a cohort of FEP patients, can predict illness course and psychopathology severity after 2 years from the onset. Moreover, we explore whether the SZ-polygenic risk score (PRS) would predict the illness course and whether the interaction between OCS and PRS shows a significant effect. A cohort of 264 FEP patients were assessed with standardized instruments. OCs were recorded using the Lewis-Murray scale in interviews with the patients' mothers: 30% of them reported at least one OC. Patients with at least one OC were more likely to have a non-remitting course of illness compared to those without OCs (35.3% vs. 16.3%, p = 0.014). No association between SZ-PRS and course of illness nor evidence for a gene-environment interaction was found. In our sample, poor short-term outcomes were associated with OCs, while SZ-PRS was not a prognostic indicator of poor outcomes.

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.

Cell type-specific and cross-population polygenic risk score analyses of MIR137 gene pathway in schizophrenia

Cell type-specific pathway-based polygenic risk scores (PRSs) may better inform disease biology and improve the precision of PRS-based clinical prediction. For microRNA-137 (MIR137), a leading neuropsychiatric risk gene and a post-transcriptional master regulator, we conducted a cell type-specific gene set PRS analysis in both European and Han Chinese schizophrenia (SZ) samples. We found that the PRS of neuronal MIR137-target genes better explains SZ risk than PRS derived from MIR137-target genes in iPSC or from the reported gene sets showing MIR137-altered expression. Compared with the PRS derived from the whole genome or the target genes of TCF4, the PRS of neuronal MIR137-target genes explained a disproportionally larger (relative to SNP number) SZ risk in the European sample, but with a more modest advantage in the Han Chinese sample. Our study demonstrated a cell type-specific polygenic contribution of MIR137-target genes to SZ risk, highlighting the value of cell type-specific pathway-based PRS analysis for uncovering disease-relevant biological features.

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PRS of neural MIR137 target genes better explains schizophrenia (SZ) risk variance

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SZ risk and SNP heritability explained by MIR137 target genes is cell type-specific

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MIR137 target genes explain a disproportionally larger SZ risk than genomic control

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PRS of MIR137 target genes better explains SZ risk in Europeans than in Han Chinese