In-Depth Notes on Schizophrenia and GWAS Findings

Overview of Schizophrenia

  • Schizophrenia is a complex condition characterized as a psychiatric, neurobiological, neurologic, neurodevelopmental, and brain disorder, often referred to as a "mental illness".

Learning Outcomes

  • After the lecture, students should be able to:

    • Explain the Genome-Wide Association Studies (GWAS) of schizophrenia.

    • Interpret key results from significant GWAS studies conducted by the Schizophrenia Working Group (SWG) of the Psychiatric Genomics Consortium (PGC) in 2014 and 2022.

    • Identify known functions of specific genes implicated in schizophrenia from the 2014 study.

Early GWAS Findings in Schizophrenia

  • ZNF804A gene:

    • Indicated as the first significant GWAS success in schizophrenia.

    • Followed a study involving 6666 patients vs. 9897 controls across multiple GWAS conducted between 2006-2008, which were below genome-wide significance.

    • Research demonstrated the risk gene's clinical and biological impacts (2017 study, Molecular Psychiatry).

  • TCF4 gene:

    • Plays a critical role in nervous system development (cited from Purcell et al., 2009).

  • Neurogranin (NRGN):

    • Expressed primarily in the brain with a focus on dendritic spines.

    • Functions as a protein kinase substrate binding to calmodulin in a calcium-free state, which is involved in neuronal calcium signaling (Shi et al., 2009).

  • Major Histocompatibility Complex (MHC) region on chromosome 6:

    • Contains genes related to immune responses (Stefansson et al., 2009).

The Schizophrenia Working Group of Psychiatric Genomics Consortium (PGC)

  • Formed in 2007 to unify global researchers for extensive meta-analyses using genome-wide genomic data for psychiatric disorders.

    • The SWG's primary goal is to consolidate available schizophrenia samples and GWAS genotypes.

First Large GWAS Study of Schizophrenia from SWG PGC (2014)

  • The largest genetic study on schizophrenia and neuropsychiatric disorders until 2022.

  • Study Composition: 36,989 cases and 113,075 controls.

  • Findings:

    • Identified 128 independent associations of SNPs across 108 loci (83 were novel).

    • Odds ratios ≤ 1.2 were noted; associations were enriched among genes expressed within the brain.

    • Notable associations include those at the DRD2 gene and genes tied to glutamatergic neurotransmission, which together could indicate pathophysiological insights and therapeutic prospects.

    • Genes associated with immune tissues emphasized the potential connection between the immune system and schizophrenia.

Genetic Insights from GWAS Studies (2014 & 2022)

  • The 2014 study utilized a Manhattan Plot illustrating 108 schizophrenia-associated loci with significance set at −log(5×10−8)=7.3-log(5 \times 10^{-8}) = 7.3.

  • Among the functional roles of identified genes are synaptic functionality, glutamatergic neurotransmission, neuronal calcium signaling, neurodevelopment, and immune processes.

Neurotransmitters Overview

  • Amino Acid Neurotransmitters:

    • Example: Glutamate (excitatory), GABA (inhibitory).

  • Biogenic Amines:

    • Includes dopamine, norepinephrine, serotonin, and histamine.

  • Neuropeptides & Gasotransmitters:

    • Various modulators impacting a broad area from their point of release.

Glutamatergic Neurotransmission Mechanisms

  • Types of Receptors:

    • Metabotropic glutamate receptors (mGluRs) are GPCRs activating biochemical cascades.

    • Ionotropic glutamate receptors (iGluRs) are ligand-gated, crucial for excitatory transmission.

    • NMDA receptors are particularly highlighted for their role in synaptic plasticity with specific subunit compositions enhancing cation-permeable channel formation.

Copy Number Variations (CNV) in Schizophrenia

  • Notable deletions associated with heightened schizophrenia risk (e.g., 22q11.2 deletion linked with DiGeorge syndrome).

  • These CNVs cluster around crucial genes involved in synaptic pathways and have implications on other neurodevelopmental disorders.

Sequencing Approaches in Schizophrenia Research

  • Next Generation Sequencing (NGS) technologies provide modern, efficient sequencing capabilities.

    • Associated with discovering de novo mutations contributing to schizophrenia risk, particularly relevant in NMDA receptor pathways.

Conclusions from 2014 & 2022 Studies

  • Genetic variations entail vast contributions to the variance in schizophrenia phenotypes.

    • Exhibits heterogeneity across patients, with all variations typically showing small effect sizes.

    • Insights gained may guide future therapeutic interventions and elucidate biological pathways involved in schizophrenia.

Genetic Insights from GWAS Studies (2014 & 2022)

The 2022 study built upon previous findings and further refined the understanding of the genetic landscape of schizophrenia.

  • Study Composition: Included larger sample sizes and more diverse cohorts, enhancing the statistical power and robustness of the findings.

  • Significant genomic loci were examined, leading to the identification of new risk variants associated with schizophrenia.

  • Functional analyses linked several of these loci to crucial biological processes, including neurotransmission and synaptic functioning.

  • The findings underscored the heterogeneity of schizophrenia, showing that genetic factors have variable impacts across different patient phenotypes.

  • Key Insights:

    • Extensions of associations observed in the 2014 study, providing a more comprehensive map of genetic risk.

    • Highlights included interactions between genes previously noted for their implications in neurotransmitter systems and new genes potentially involved in the immune response.

    • The inclusion of data from diverse populations offered a glimpse into the potential influence of ethnicity on genetic predisposition and schizophrenia risk.

Conclusions from the 2022 study emphasize that genetic variations contribute extensively to schizophrenia's variance, guiding potential future therapeutic interventions and deepening the understanding of biological pathways involved in this complex disorder.

Known Functions of Specific Genes Implicated in Schizophrenia from GWAS Studies
Genes from the 2014 Study

  • ZNF804A gene: Indicated as the first significant GWAS success in schizophrenia. Demonstrated clinical and biological impacts.

  • TCF4 gene: Plays a critical role in nervous system development (cited from Purcell et al., 2009).

  • Neurogranin (NRGN): Expressed primarily in the brain with a focus on dendritic spines. Functions as a protein kinase substrate binding to calmodulin in a calcium-free state, involved in neuronal calcium signaling (Shi et al., 2009).

  • Major Histocompatibility Complex (MHC) region on chromosome 6: Contains genes related to immune responses (Stefansson et al., 2009).

Genes from the 2022 Study

  • Significant genomic loci identified provided further understanding of genetic variations associated with schizophrenia, linking several of these loci to crucial biological processes including:

    • Neurotransmission: Genes involved in synaptic functionality and glutamatergic neurotransmission.

    • Synaptic Functioning: Enhanced understanding of how genetic variants impact the efficiency and effectiveness of synaptic transmission.

    • Immune Response: Some new risk variants were connected