Whole-genome analysis in Korean patients with autoimmune myasthenia gravis

Assessing the lack of diversity in genetics research across neurodegenerative diseases: a systematic review of the GWAS Catalog and literature

Importance

The under-representation of participants with non-European ancestry in genome-wide association studies (GWAS) is a critical issue that has significant implications, including hindering the progress of precision medicine initiatives. This issue is particularly significant in the context of neurodegenerative diseases (NDDs), where current therapeutic approaches have shown limited success. Addressing this under-representation is crucial to harnessing the full potential of genomic medicine in underserved communities and improving outcomes for NDD patients.

Objective

Our primary objective was to assess the representation of non-European ancestry participants in genetic discovery efforts related to NDDs. We aimed to quantify the extent of inclusion of diverse ancestry groups in NDD studies and determine the number of associated loci identified in more inclusive studies. Specifically, we sought to highlight the disparities in research efforts and outcomes between studies predominantly involving European ancestry participants and those deliberately targeting non-European or multi-ancestry populations across NDDs.

Evidence Review

We conducted a systematic review utilizing existing GWAS results and publications to assess the inclusion of diverse ancestry groups in neurodegeneration and neurogenetics studies. Our search encompassed studies published up to the end of 2022, with a focus on identifying research that deliberately included non-European or multi-ancestry cohorts. We employed rigorous methods for the inclusion of identified articles and quality assessment.

Findings

Our review identified a total of 123 NDD GWAS. Strikingly, 82% of these studies predominantly featured participants of European ancestry. Endeavors specifically targeting non-European or multi-ancestry populations across NDDs identified only 52 risk loci. This contrasts with predominantly European studies, which reported over 90 risk loci for a single disease. Encouragingly, over 65% of these discoveries occurred in 2020 or later, indicating a recent increase in studies deliberately including non-European cohorts.

Conclusions and relevance

Our findings underscore the pressing need for increased diversity in neurodegenerative research. The significant under-representation of non-European ancestry participants in NDD GWAS limits our understanding of the genetic underpinnings of these diseases. To advance the field of neurodegenerative research and develop more effective therapies, it is imperative that future investigations prioritize and harness the genomic diversity present within and across global populations.

Myasthenia gravis genome-wide association study implicates AGRN as a risk locus

BACKGROUND

Myasthenia gravis (MG) is a rare autoimmune disorder affecting the neuromuscular junction (NMJ). Here, we investigate the genetic architecture of MG via a genome-wide association study (GWAS) of the largest MG data set analysed to date.

METHODS

We performed GWAS meta-analysis integrating three different data sets (total of 1401 cases and 3508 controls). We carried out human leucocyte antigen (HLA) fine-mapping, gene-based and tissue enrichment analyses and investigated genetic correlation with 13 other autoimmune disorders as well as pleiotropy across MG and correlated disorders.

RESULTS

We confirmed the previously reported MG association with TNFRSF11A (rs4369774; p=1.09×10^-13, OR=1.4). Furthermore, gene-based analysis revealed AGRN as a novel MG susceptibility gene. HLA fine-mapping pointed to two independent MG loci: HLA-DRB1 and HLA-B. MG onset-specific analysis reveals differences in the genetic architecture of early-onset MG (EOMG) versus late-onset MG (LOMG). Furthermore, we find MG to be genetically correlated with type 1 diabetes (T1D), rheumatoid arthritis (RA), late-onset vitiligo and autoimmune thyroid disease (ATD). Cross-disorder meta-analysis reveals multiple risk loci that appear pleiotropic across MG and correlated disorders.

DISCUSSION

Our gene-based analysis identifies AGRN as a novel MG susceptibility gene, implicating for the first time a locus encoding a protein (agrin) that is directly relevant to NMJ activation. Mutations in AGRN have been found to underlie congenital myasthenic syndrome. Our results are also consistent with previous studies highlighting the role of HLA and TNFRSF11A in MG aetiology and the different risk genes in EOMG versus LOMG. Finally, we uncover the genetic correlation of MG with T1D, RA, ATD and late-onset vitiligo, pointing to shared underlying genetic mechanisms.

Evidence for association of STAT4 and IL12RB2 variants with Myasthenia gravis susceptibility: What is the effect on gene expression in thymus?

Myasthenia gravis (MG) is an autoimmune disease mediated by the presence of autoantibodies that bind mainly to the acetylcholine receptor (AChR) in the neuromuscular junction. In our case-control association study, we analyzed common variants located in genes of the IL12/STAT4 and IL10/STAT3 signaling pathways. A total of 175 sporadic MG patients of Greek descent, positively detected with anti-AChR autoantibodies and 84 ethnically-matched, healthy volunteers were enrolled in the study. Thymus samples were obtained from 16 non-MG individuals for relative gene expression analysis. The strongest signals of association were observed in the cases of rs6679356 between the late-onset MG patients and controls and rs7574865 between early-onset MG and controls. Our investigation of the correlation between the MG-associated variants and the expression levels of each gene in thymus did not result in significant differences.

The Minor Variant of the Single-Nucleotide Polymorphism rs3753381 Affects the Activity of a SLAMF1 Enhancer

The SLAMF1 gene encodes CD150, a transmembrane glycoprotein expressed on the surface of T and B-lymphocytes, NK-cells, dendritic cells, and subpopulations of macrophages and basophils. We investigated the functional regulatory polymorphisms of the SLAMF1 locus associated with autoimmune processes, using bioinformatics and a mutational analysis of the regulatory elements overlapping with polymorphic positions. In the reporter gene assay in MP-1 and Raji B-cell lines, the enhancer activity of the regulatory region of the locus containing the rs3753381 polymorphism demonstrated a twofold increase upon the introduction of the rs3753381 minor variant (G → A) associated with myasthenia gravis. An analysis of the nucleotide context in the vicinity of rs3753381 revealed that the minor version of this polymorphism improves several binding sites for the transcription factors of FOX and NFAT, and RXR nuclear receptors. All mutations that disrupt any of these sites lead to a decrease in the enhancer activity both in MP1 and in Raji cells, and each of the two B-cell lines expresses a specific set of these factors. Thus, the minor variant of the rs3753381 polymorphism may contribute to the development of myasthenia gravis by modulating SLAMF1 expression, presumably in pathogenic B-lymphocytes.

Juvenile Myasthenia Gravis in Korea: Subgroup Analysis According to Sex and Onset Age

Juvenile myasthenia gravis presents before 18 years of age with different characteristics according to racial background and pubertal development. The authors aimed to determine the clinical characteristics of children and adolescents of Korean ethnicity with myasthenia gravis, and evaluate the presentation and clinical outcomes according to the sex and onset age of the patients. The authors recruited 88 Korean juvenile myasthenia gravis patients between September 2005 and August 2015. Worse clinical severity from presentation, more aggressive treatment strategies, and worse final treatment outcomes were noted in girls with postpubertal onset than in the other patients. The symptoms were milder (pure ocular presentation in 96.6% [85/88]) and the disease course was more benign (94.3% [83/88]) in this study than in the literature. The homogenous racial background might have contributed to these results. These findings highlight the influence of pubertal development and the need for timely and appropriate active treatment, including thymectomy, to improve prognosis.

Early B-cell factor 1 (EBF1) is critical for transcriptional control of SLAMF1 gene in human B cells

Signaling lymphocytic activation molecule family member 1 (SLAMF1)/CD150 is a co-stimulatory receptor expressed on a variety of hematopoietic cells, in particular on mature lymphocytes activated by specific antigen, costimulation and cytokines. Changes in CD150 expression level have been reported in association with autoimmunity and with B-cell chronic lymphocytic leukemia. We characterized the core promoter for SLAMF1 gene in human B-cell lines and explored binding sites for a number of transcription factors involved in B cell differentiation and activation. Mutations of SP1, STAT6, IRF4, NF-kB, ELF1, TCF3, and SPI1/PU.1 sites resulted in significantly decreased promoter activity of varying magnitude, depending on the cell line tested. The most profound effect on the promoter strength was observed upon mutation of the binding site for Early B-cell factor 1 (EBF1). This mutation produced a 10-20 fold drop in promoter activity and pinpointed EBF1 as the master regulator of human SLAMF1 gene in B cells. We also identified three potent transcriptional enhancers in human SLAMF1 locus, each containing functional EBF1 binding sites. Thus, EBF1 interacts with specific binding sites located both in the promoter and in the enhancer regions of the SLAMF1 gene and is critical for its expression in human B cells.