HLA typing using genome wide data reveals susceptibility types for infections in a psychiatric disease enriched sample

NOVEL SIMPLEXVIRUS (SIMPLEXVIRUS DOLICHOTINEALPHA1) ASSOCIATED WITH FATALITY IN FOUR PATAGONIAN MARA (DOLICHOTIS PATAGONUM)

Four of seven Patagonian maras (Dolichotis patagonum) at a zoological institution developed acute neurologic signs that progressed to tetraparesis and death. All affected were young adult females (10 mon-5 yr old) that presented over 11 d. Clinical signs were rapidly progressive and unresponsive to supportive therapies. Two of the four individuals were found deceased 4 d after hospitalization. Two individuals were euthanized due to poor prognosis and decline after 6 and 8 d, respectively. Simultaneously, an additional mara developed mild and self-resolving clinical signs, including a kyphotic gait and paraparesis. On gross examination, there were widespread petechiae and ecchymoses of the skeletal muscle, myocardium, skin, pericardium, urinary bladder mucosa, and spinal cord. On histopathology, all animals had necrotizing myelitis and rhombencephalitis, with intranuclear viral inclusions in three individuals. Electron microscopy confirmed herpesviral replication and assembly complexes in neurons and oligodendrocytes. Consensus PCR performed on spinal cord, brainstem, or cerebellum revealed a novel Simplexvirus most closely related to Simplexvirus leporidalpha 4. The virus was amplified and sequenced and is referred to as Simplexvirus dolichotinealpha1. It is unknown whether this virus is endemic in Patagonian mara or whether it represents an aberrant host species. Clinicians should be aware of this virus and its potential to cause severe, rapidly progressive, life-threatening disease in this species.

Genetic risk for hospitalization of African American patients with severe mental illness reveals HLA loci

Background

Mood disorders such as major depressive and bipolar disorders, along with posttraumatic stress disorder (PTSD), schizophrenia (SCZ), and other psychotic disorders, constitute serious mental illnesses (SMI) and often lead to inpatient psychiatric care for adults. Risk factors associated with increased hospitalization rate in SMI (H-SMI) are largely unknown but likely involve a combination of genetic, environmental, and socio-behavioral factors. We performed a genome-wide association study in an African American cohort to identify possible genes associated with hospitalization due to SMI (H-SMI).

Methods

Patients hospitalized for psychiatric disorders (H-SMI; n=690) were compared with demographically matched controls (n=4467). Quality control and imputation of genome-wide data were performed following the Psychiatric Genetic Consortium (PGC)-PTSD guidelines. Imputation of the Human Leukocyte Antigen (HLA) locus was performed using the HIBAG package.

Results

Genome-wide association analysis revealed a genome-wide significant association at 6p22.1 locus in the ubiquitin D (UBD/FAT10) gene (rs362514, p=9.43x10-9) and around the HLA locus. Heritability of H-SMI (14.6%) was comparable to other psychiatric disorders (4% to 45%). We observed a nominally significant association with 2 HLA alleles: HLA-A*23:01 (OR=1.04, p=2.3x10-3) and HLA-C*06:02 (OR=1.04, p=1.5x10-3). Two other genes (VSP13D and TSPAN9), possibly associated with immune response, were found to be associated with H-SMI using gene-based analyses.

Conclusion

We observed a strong association between H-SMI and a locus that has been consistently and strongly associated with SCZ in multiple studies (6p21.32-p22.1), possibly indicating an involvement of the immune system and the immune response in the development of severe transdiagnostic SMI.

The impact of HLA polymorphism on herpesvirus infection and disease

Human Leukocyte Antigens (HLA) are cell surface molecules, central in coordinating innate and adaptive immune responses, that are targets of strong diversifying natural selection by pathogens. Of these pathogens, human herpesviruses have a uniquely ancient relationship with our species, where coevolution likely has reciprocating impact on HLA and viral genomic diversity. Consistent with this notion, genetic variation at multiple HLA loci is strongly associated with modulating immunity to herpesvirus infection. Here, we synthesize published genetic associations of HLA with herpesvirus infection and disease, both from case/control and genome-wide association studies. We analyze genetic associations across the eight human herpesviruses and identify HLA alleles that are associated with diverse herpesvirus-related phenotypes. We find that whereas most HLA genetic associations are virus- or disease-specific, HLA-A*01 and HLA-A*02 allotypes may be more generally associated with immune susceptibility and control, respectively, across multiple herpesviruses. Connecting genetic association data with functional corroboration, we discuss mechanisms by which diverse HLA and cognate receptor allotypes direct variable immune responses during herpesvirus infection and pathogenesis. Together, this review examines the complexity of HLA-herpesvirus interactions driven by differential T cell and Natural Killer cell immune responses.

Association between toxoplasmosis and bipolar disorder: A systematic review and meta-analysis

BACKGROUND

The relationship between toxoplasma gondii (T. gondii) infection and bipolar disorder (BD) is poorly understood. This review explores this relationship by estimating the strength of the association between the two conditions using data from published studies.

METHODS

Following PRISMA guidelines, we performed a review and meta-analysis of published articles obtained from a systematic search of PubMed, PsycINFO, EMBASE and the Cochrane library up to January 10th, 2021. We included observational studies that compared seroprevalence of IgG class antibodies against T. gondii in patients with a diagnosis of BD with healthy controls. We excluded studies that included <10 participants in each study arm and patients with a serious concomitant medical illness. Discrepancies between the two independent researchers were resolved by consulting a third experienced researcher. Summary data were extracted from published reports. Analysis was conducted using both fixed-effects and random-effects models. The study is registered with PROSPERO number CRD42021237809.

FINDINGS

The search yielded 23 independent studies with a total of 12690 participants (4021 with BD and 8669 controls). Persons with BD had a greater odd of seropositivity with toxoplasmosis than controls, both in the fixed-effects model (OR = 1.34 [95%CI: 1.19 to 1.51]) and the random-effects model (OR = 1.69 [95%CI: 1.21 to 2.36]). No publication bias was detected but reported results showed a high heterogeneity (I2 = 84% [95%CI:77%-89%]).

INTERPRETATION

The findings support the relationship between toxoplasmosis infection and BD and suggests a need for studies designed to explore possible causal relationship. Such studies may also improve our understanding of the pathophysiology of BD and open other avenues for its treatment.

FUNDING

P.O.R. Sardegna F.S.E. 2014-2020.

Impact of SARS-CoV-2 on Host Factors Involved in Mental Disorders

COVID-19, caused by SARS-CoV-2, is a systemic illness due to its multiorgan effects in patients. The disease has a detrimental impact on respiratory and cardiovascular systems. One early symptom of infection is anosmia or lack of smell; this implicates the involvement of the olfactory bulb in COVID-19 disease and provides a route into the central nervous system. However, little is known about how SARS-CoV-2 affects neurological or psychological symptoms. SARS-CoV-2 exploits host receptors that converge on pathways that impact psychological symptoms. This systemic review discusses the ways involved by coronavirus infection and their impact on mental health disorders. We begin by briefly introducing the history of coronaviruses, followed by an overview of the essential proteins to viral entry. Then, we discuss the downstream effects of viral entry on host proteins. Finally, we review the literature on host factors that are known to play critical roles in neuropsychiatric symptoms and mental diseases and discuss how COVID-19 could impact mental health globally. Our review details the host factors and pathways involved in the cellular mechanisms, such as systemic inflammation, that play a significant role in the development of neuropsychological symptoms stemming from COVID-19 infection.

Polygenic risk scores differentiate schizophrenia patients with toxoplasma gondii compared to toxoplasma seronegative patients

Schizophrenia (SCZ) is an etiologically heterogeneous disease with genetic and environmental risk factors (e.g., Toxoplasma gondii infection) differing among affected individuals. Distinguishing such risk factors may point to differences in pathophysiological pathways and facilitate the discovery of individualized treatments. Toxoplasma gondii (TOXO) has been implicated in increasing the risk of schizophrenia. To determine whether TOXO-positive individuals with SCZ have a different polygenic risk burden than uninfected people, we applied the SCZ polygenic risk score (SCZ-PRS) derived from the Psychiatric GWAS Consortium separately to the TOXO-positive and TOXO-negative subjects with the diagnosis of SCZ as the outcome variable. The SCZ-PRS does not include variants in the major histocompatibility complex. Of 790 subjects assessed for TOXO, the 662 TOXO-negative subjects (50.8% with SCZ) reached a Bonferroni corrected significant association (p = 0.00017, R² = 0.023). In contrast, the 128 TOXO-positive individuals (53.1% with SCZ) showed no significant association (p = 0.354) for SCZ-PRS and had a much lower R² (R² = 0.007). To account for Type-2 error in the TOXO-positive dataset, we performed a random sampling of the TOXO-negative subpopulation (n = 130, repeated 100 times) to simulate equivalent power between groups: the p-value was <0.05 for SCZ-PRS 55% of the time but was rarely (6% of the time) comparable to the high p-value of the seropositive group at p > 0.354. We found intriguing evidence that the SCZ-PRS predicts SCZ in TOXO-negative subjects, as expected, but not in the TOXO-positive individuals. This result highlights the importance of considering environmental risk factors to distinguish a subgroup with independent or different genetic components involved in the development of SCZ.

Association of HLA locus alleles with posttraumatic stress disorder

BACKGROUND

Immune dysregulation has been widely observed in those with posttraumatic stress disorder (PTSD). An individual's immune response is shaped, in part, by the highly polymorphic Human Leukocyte Antigen (HLA) locus that is associated with major psychiatric disorders such as schizophrenia, major depression and bipolar disorder. The aim of the current study was to investigate the association between common HLA alleles and PTSD.

METHODS

Genome-wide association data was used to predict alleles of 7 classical polymorphic HLA genes (A, B, C, DRB1, DQA1, DQB1, DPB1) in 403 lifetime PTSD cases and 369 trauma exposed controls of African ancestry. Association of HLA allelic variations with lifetime PTSD was analyzed using logistic regression, controlling for ancestry, sex and multiple comparisons. The effect of HLA alleles on gene expression was assessed by weighted correlation network analysis (WGCNA), using 353 subjects with available expression data. Enrichment analysis was performed using anRichment to identify associated pathways of each module.

RESULTS

HLA-B*58:01 (p = 0.035), HLA-C*07:01 (p = 0.035), HLA-DQA1*01:01 (p = 0.003), HLA-DQB1*05:01 (p = 0.009) and HLA-DPB1*17:01 (p = 0.017) were more common in PTSD cases, while HLA-A*02:01 (p = 0.026), HLA-DQA1*05:05 (p = 0.011) and HLA-DRB1*11:01 (p < 0.001) were more frequent in controls. WGCNA was used to explore expression patterns of the PTSD related alleles. Gene expression modules of PTSD-related HLA alleles were enriched in various pathways, including pathways related to immune and neural activity.

CONCLUSIONS

To the best of our knowledge, this is the first study to report an association of HLA alleles with PTSD. Altogether, our results support the link between the immune system, brain and PTSD.

Genome-wide association study in two populations to determine genetic variants associated with Toxoplasma gondii infection and relationship to schizophrenia risk

T. gondii (TOXO) infects over one billion people worldwide, yet the literature lacks a Genome Wide Association Study (GWAS) focused on genetic variants controlling the persistence of TOXO infection. To identify putative T. gondii susceptibility genes, we performed a GWAS using IgG seropositivity as the outcome variable in a discovery sample (n = 790) from an Ashkenazi dataset, and a second sample of predominately African Americans (The Grady Trauma Project, n = 285). We also performed a meta-analyses of the 2 cohorts. None of the SNPs in these analyses was statistically significant after Bonferroni correction for multiple comparisons. In the Ashkenazi population, the gene region of CHIA (chitinase) showed the most nominally significant association with TOXO. Prior studies have shown that the production of chitinase by macrophages in the brain responding to TOXO infection is crucial for controlling the burden of T. gondii cysts. We found a surprising number of genes involved in neurodevelopment and psychiatric disorders among our top hits even though our outcome variable was TOXO infection. In the meta-analysis combining the Ashkenazi and Grady Trauma Project samples, there was enrichment for genes implicated in schizophrenia spectrum disorders (p < .05). Upon limiting our sample to those without mental illness, two schizophrenia related genes (CNTNAP2, GABAR2) still had significant TOXO-associated variants at the p < .05 level, but did not pass the genome wide significance threshold after correction for multiple comparisons. Using Ingenuity Systems molecular network analysis, we identified molecular nodes suggesting that while different genetic variants associated with TOXO in the two population samples, the molecular pathways for TOXO susceptibility nevertheless converged on common pathways. Molecular nodes in these common pathways included NOTCH1, CD44, and RXRA. Prior studies show that CD44 participates in TOXO-induced immunopathology and that RXRA is instrumental in regulating T-helper immune responses. These data provide new insights into the pathophysiology of this common neurotropic parasite.

From Infection to the Microbiome: An Evolving Role of Microbes in Schizophrenia

The study of microorganisms such as bacteria, viruses, archaea, fungi, and protozoa in the context of psychiatric disorders may be surprising to some. This intersection of disciplines, however, has a rich history and is currently revitalized by newfound functions of the microbiome and the gut-brain axis in human diseases. Schizophrenia, in particular, fits this model as a disorder with gene and environmental roots that may be anchored in the immune system. In this context, the combination of a precisely timed pathogen exposure in a person with genetically encoded altered immunity may have especially destructive consequences for the central nervous system (CNS). Furthermore, significant components of immunity, such as the development of the immune response and the concept of immune tolerance, are largely dictated by the commensal residents of the microbiome. When this community of microbes is imbalanced, perhaps as the result of a pathogen invasion, stress, or immune gene deficiency, a pathological cycle of localized inflammation, endothelial barrier compromise, translocation of gut-derived products, and systemic inflammation may ensue. If these pathologies enable access of gut and microbial metabolites and immune molecules to the CNS across the blood-brain barrier (BBB), and studies of the gut-brain axis support this hypothesis, a worsening of cognitive deficits and psychiatric symptoms is predicted to occur in susceptible individuals with schizophrenia. In this chapter, we review the role of microbes in various stages of this model and how these organisms may contribute to documented phenotypes of schizophrenia. An increased understanding of the role of pathogens and the microbiome in psychiatric disorders will better guide the development of microbial and immune-based therapeutics for disease prevention and treatment.

Deciphering microbiome and neuroactive immune gene interactions in schizophrenia

The body's microbiome represents an actively regulated network of novel mechanisms that potentially underlie the etiology and pathophysiology of a wide range of diseases. For complex brain disorders such as schizophrenia, understanding the cellular and molecular pathways that intersect the bidirectional gut-brain axis is anticipated to lead to new methods of treatment. The means by which the microbiome might differ across neuropsychiatric and neurological disorders are not known. Brain disorders as diverse as schizophrenia, major depression, Parkinson's disease and multiple sclerosis appear to share a common pathology of an imbalanced community of commensal microbiota, often measured in terms of a leaky gut phenotype accompanied by low level systemic inflammation. While environmental factors associated with these disease states might contribute to intestinal pathologies, products from a perturbed microbiome may also directly promote specific signs, symptoms and etiologies of individual disorders. We hypothesize that in schizophrenia, it is the putatively unique susceptibility related to genes that modulate the immune system and the gut-brain pleiotropy of these genes which leads to a particularly neuropathological response when challenged by a microbiome in dysbiosis. Consequences from exposure to this dysbiosis may occur during pre- or post-natal time periods and thus may interfere with normal neurodevelopment in those who are genetically predisposed. Here, we review the evidence from the literature which supports the idea that the intersection of the microbiome and immune gene susceptibility in schizophrenia is relevant etiologically and for disease progression. Figuring prominently at both ends of the gut-brain axis and at points in between are proteins encoded by genes found in the major histocompatibility complex (MHC), including select MHC as well as non-MHC complement pathway genes.