Integrating Genomics and Mendelian Randomization to Uncover Microglial Drug Targets in Multiple Sclerosis
Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the central nervous system in which immune dysregulation, demyelination, and tissue injury unfold in parallel. The article by Yan, Wen, and Jianhong addresses a central question in contemporary MS biology: which microglia-associated genes are not merely correlated with disease, but may also contribute causally to disease susceptibility and therefore represent plausible therapeutic targets. This focus is scientifically important because microglia occupy a dual position in MS pathology. They can amplify injury through inflammatory signalling, but they may also support debris clearance, remyelination, and tissue repair. By concentrating on microglial gene regulation rather than on broad immune associations alone, the study attempts to refine the search for biologically meaningful and pharmacologically actionable targets in MS.
Integrative Design: Combining Transcriptomics, eQTLs, and Causal Inference
The strength of the study lies in its integrative design. The authors combined bulk RNA sequencing from chronic active MS lesions (GSE108000), single-nucleus RNA sequencing from MS plaque tissue (GSE227781), cis-eQTL data from the eQTLGen Consortium, and large-scale MS genome-wide association data from the International Multiple Sclerosis Genetics Consortium. They then applied two-sample Mendelian randomization (MR), followed by sensitivity analyses, summary-data-based Mendelian randomization (SMR), Bayesian colocalization, methylation analysis, and protein–protein interaction mapping. This layered strategy is notable because each method addresses a different inferential gap: differential expression identifies candidate biology, eQTLs connect variants to transcription, MR tests putative causal directionality, SMR and HEIDI assess pleiotropy-related concerns, and colocalization asks whether the same underlying variant likely drives both gene expression and disease association.
Transcriptomic Screening: From Thousands of Signals to a Focused Gene Set
The transcriptomic component provided the initial biological filter. In the bulk RNA-seq dataset, the authors identified 428 significantly upregulated and 209 significantly downregulated mRNAs in MS microglia relative to healthy white matter. In the single-cell dataset, they found 721 significantly upregulated mRNAs in MS microglia after cell-level quality control, normalization, clustering, and marker-based annotation. When these expression results were intersected with the eQTL-informed MR findings, seven genes emerged in common: ARHGAP25, HLA-DRB1, MERTK, MS4A6A, SAMSN1, SYK, and XBP1. This convergence across lesion-level transcriptomics, single-cell profiling, and genetic regulation is important because it reduces the likelihood that the highlighted genes are artifacts of a single platform or dataset.
Mendelian Randomization Results: Five Genes Associated With Increased MS Risk
The decisive step in the paper was the MR analysis of 15,695 eQTL genes. Using inverse-variance weighting and related MR estimators, the authors found that increased expression of five genes was associated with higher MS risk: ARHGAP25 (OR 1.45), HLA-DRB1 (OR 2.24), MERTK (OR 1.10), MS4A6A (OR 1.16), and SYK (OR 1.13). Two other genes, SAMSN1 and XBP1, showed odds ratios below 1, suggesting possible protective effects, but because those directions conflicted with the observed expression patterns in the lesion datasets, they were removed from downstream prioritization. Importantly, the instrumental variables had F-statistics exceeding conventional weak-instrument thresholds, and no pleiotropy was detected for the five prioritized genes by MR-Egger intercept testing, although heterogeneity was present for HLA-DRB1 and SYK, indicating that these two loci may involve more complex genetic architecture.
Convergent Evidence Elevates HLA-DRB1 and SYK
Among the five prioritized genes, HLA-DRB1 and SYK received the strongest cumulative support. SMR analysis indicated that HLA-DRB1 expression was associated with MS in both whole blood and brain tissue, although the HEIDI result suggested tissue-specific complexity, with evidence against pleiotropy in whole blood but possible pleiotropy in brain tissue. Bayesian colocalization then provided especially compelling evidence: the posterior probability for a shared causal variant was 100.00% for HLA-DRB1 and 97.93% for SYK. In practical terms, this means that these loci are not only associated with MS and with altered expression, but may be driven by the same underlying genetic signals. The study therefore presents HLA-DRB1 as the most strongly supported target overall, while positioning SYK as a second highly credible candidate with translational relevance.
Biological Interpretation: Immune Presentation, Phagocytic Control, and Drug Repurposing
The biological interpretation of the candidate genes is one of the paper’s most valuable contributions. HLA-DRB1 is already well known in MS genetics, and here it is reframed within a microglial regulatory context involving antigen presentation, inflammatory modulation, and methylation-sensitive expression control. MERTK is discussed as a regulator of efferocytosis and inflammatory resolution, consistent with the idea that defective clearance and maladaptive repair responses contribute to lesion persistence. ARHGAP25 is linked to cytoskeletal regulation, phagocytosis, and NF-κB-related inflammatory signalling, while MS4A6A is interpreted as a modulator of microglial activation with parallels to other neurodegenerative disorders. SYK is particularly attractive pharmacologically because DrugBank analysis identified numerous compounds linked to it, whereas MERTK was associated with a smaller set of agents; by contrast, ARHGAP25, HLA-DRB1, and MS4A6A lacked approved drugs in the database surveyed. These results suggest a realistic repurposing path for SYK- and MERTK-directed therapies, even if direct MS-specific efficacy remains unproven.
Significance, Limitations, and Future Directions
Overall, this article is a strong example of modern target discovery in neuroimmunology. Rather than relying solely on differential expression or GWAS proximity, it assembles a multi-layered evidentiary framework that moves from association toward causality and therapeutic plausibility. Its principal contribution is the prioritization of five microglia-associated genes, with HLA-DRB1 and SYK standing out as the most strongly supported targets and MERTK emerging as an additional candidate with plausible druggability. At the same time, the authors appropriately acknowledge key limitations: the study depends heavily on publicly available datasets, which may not capture full population diversity, and the causal inferences remain statistical until validated experimentally in cellular and animal models. For that reason, the paper should be seen not as a final statement on MS therapeutics, but as a rigorous roadmap for mechanistic follow-up, biomarker refinement, and rational drug development in microglia-centered MS research.
Significance, Limitations, and Future Directions
Overall, this article makes a meaningful contribution by proposing ACE2 as both a serum biomarker candidate and a susceptibility gene in MS within a Jordanian population. Its principal strength lies in combining biochemical and genetic evidence in the same study framework. Nevertheless, the authors are appropriately cautious: the serum protein analysis was performed in a relatively small subset, longitudinal samples were unavailable, and only two ACE2 SNPs were examined, limiting broader haplotypic interpretation. These constraints mean that the work should be viewed as a strong hypothesis-generating study rather than definitive proof of clinical utility. Future research should test these findings in larger and ethnically diverse cohorts, include more progressive MS cases, and use longitudinal sampling to determine whether ACE2 predicts relapse activity, disability progression, or therapeutic response. In that sense, the study opens an important line of investigation at the intersection of neuroimmunology, cardiovascular signaling biology, and precision medicine in MS.
Disclaimer: This blog post is based on the provided research article and is intended for informational purposes only. It is not intended to provide medical advice. Please consult with a healthcare professional for any health concerns.
References:
Al-Keilani, M.S., Abdelrazeq, H.M., Hendi, N.N. et al. Association of angiotensin converting enzyme type 2 serum level and gene polymorphisms with multiple sclerosis. Sci Rep 16, 10690 (2026). https://doi.org/10.1038/s41598-026-46187-5
