Towards an Inclusive Genomic Understanding of Multiple Sclerosis

Jacobs and colleagues argue that multiple sclerosis genetics remains scientifically incomplete because most genome-wide association studies have been conducted in populations of European ancestry. This imbalance is striking: individuals of European ancestry represent only a minority of the global population, yet they dominate GWAS cohorts, while Asian, African, and other ancestries remain substantially under-represented. In MS, European-ancestry studies have identified 32 independent MHC signals, 200 autosomal loci, and one X chromosome locus, collectively explaining up to approximately half of estimated genetic heritability. However, these findings cannot automatically be generalized to populations with different allele frequencies, haplotypes, linkage disequilibrium patterns, and environmental exposures. The article therefore frames diversity in MS genomics not as a peripheral equity issue, but as a prerequisite for a valid biological understanding of the disease.

Epidemiology at the Interface of Genes and Environment
The authors emphasize that global variation in MS prevalence cannot be interpreted solely through genetics. Reported age-standardized prevalence ranges from very low estimates in Oceania and central sub-Saharan Africa to much higher estimates in high-income North America, but these differences are confounded by diagnostic access, ascertainment bias, MRI availability, health-record infrastructure, and environmental exposures. Rapid epidemiological shifts, such as the reported doubling of MS incidence among women of East Asian or South East Asian descent in British Columbia between 1986 and 2010, strongly suggest that non-genetic factors also shape disease risk. A pan-ancestral genetic map could help distinguish true biological risk from underdiagnosis and could even estimate the “hidden burden” of MS in settings where neurological services are limited.

The MHC Locus as a Cross-Ancestral Laboratory
The major histocompatibility complex remains the strongest genetic region implicated in MS susceptibility, but its interpretation is complicated by dense gene content, long-range haplotypes, and population-specific HLA allele distributions. The article highlights that HLA-DRB115:01 has the largest effect on MS risk in European populations, while Figure 1 shows clear global variation in its allele frequency, with relative rarity in Africa and South Asia and higher frequencies in North America, Scandinavia, and Central Europe. Cross-ancestral studies are valuable because they can separate alleles that are tightly linked in one ancestry but not in another. For example, evidence from African American and Martinican cohorts helped clarify that the DRB115:01–DQB106:02 haplotype association is primarily driven by DRB115 alleles.

Beyond the MHC: Shared Signals and Novel Loci
Outside the MHC, many MS-associated variants discovered in European populations appear to have broadly similar effects across ancestries, but the article cautions that true ancestry-specific heterogeneity is difficult to detect without large samples and appropriate genotyping platforms. Existing studies in African American, Hispanic, South Asian, Japanese, Sardinian, and other cohorts have often focused on replication rather than discovery, partly because non-European MS cohorts remain underpowered. Nevertheless, ancestry-informed research can reveal loci that would otherwise remain obscure. The Sardinian BAFF/TNFSF13B example is particularly instructive: population-specific linkage disequilibrium and allele-frequency patterns enabled discovery of a variant affecting soluble BAFF levels, B-cell biology, and MS susceptibility. This demonstrates that discoveries in one genetic isolate or ancestry group can illuminate mechanisms relevant to MS biology more broadly.

Phenotypic Diversity and Disease Severity
The article also connects ancestry to MS clinical heterogeneity. Although GWAS has explained little of the variation in disease course, age at onset, relapse burden, disability accumulation, and progression may still have genetic components that require more diverse sampling to detect. Evidence summarized by the authors indicates that individuals of African ancestry, often approximated through Black ethnicity in epidemiological datasets, may experience greater disability at diagnosis, faster progression, higher morbidity and mortality, and poorer responses to disease-modifying therapies than individuals of European ancestry. These observations must be interpreted carefully because social determinants, structural racism, differential access to care, and clinical ascertainment biases may contribute substantially. Even so, larger multi-ancestry genetic studies could help distinguish biological contributors to severity from remediable inequities in diagnosis and treatment.

From GWAS to Clinical Translation
A central translational message of the article is that GWAS findings are not endpoints; they are inputs for polygenic risk scores, Mendelian randomization, heritability partitioning, functional annotation, and fine mapping. Polygenic risk scores derived from European-ancestry GWAS often perform poorly in non-European populations because allele frequencies, linkage disequilibrium, and marginal effect estimates differ across ancestries. Similarly, Mendelian randomization analyses require ancestry-matched exposure and outcome datasets to avoid biased inference. Figure 2 illustrates why cross-ancestral fine mapping is powerful: the lead variant at a locus can differ between ancestries, but combining association patterns across populations can narrow the credible interval around the likely causal variant. Thus, diverse GWAS are essential for both equitable prediction and mechanistic discovery.

Ethical, Logistical, and Scientific Imperatives
The authors conclude that expanding MS genetics beyond European-ancestry cohorts is both an ethical responsibility and a scientific necessity. The challenges are substantial: large sample sizes are required, genotyping arrays designed for European populations may be inadequate, ancestry-matched controls are difficult to assemble, and historical abuses have created justified mistrust toward genetic research in some communities. The article therefore calls for careful study design, local scientific leadership, sustained participant involvement, respectful communication, and infrastructure-building rather than extractive research. Its final argument is clear: consortium-scale, ancestrally inclusive MS genetics has the potential to refine causal biology, improve prediction, reduce disparities, and benefit people with MS from all ancestral backgrounds.

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:
Jacobs, B. M., Peter, M., Giovannoni, G., Noyce, A. J., Morris, H. R., & Dobson, R. (2022). Towards a global view of multiple sclerosis genetics. Nature Reviews Neurology, 18(10), 613-623.