Expanding the Genetic Map of Multiple Sclerosis Across Global Populations
The Perspective article “Towards a global view of multiple sclerosis genetics” addresses a fundamental limitation in contemporary human genomics: the systematic under-representation of populations with non-European ancestry. Although individuals of European ancestry constitute approximately 16% of the global population, they account for nearly 78% of participants included in genome-wide association studies, whereas participants of Asian and African ancestry represent only about 11% and 2.4%, respectively. This imbalance is particularly consequential in multiple sclerosis (MS), a neuroimmunological disorder with a substantial heritable component. Studies conducted predominantly in European populations have identified 32 independent susceptibility signals within the major histocompatibility complex (MHC), approximately 200 additional autosomal loci and one locus on the X chromosome, collectively explaining as much as half of the estimated genetic heritability of MS. However, these discoveries cannot automatically be assumed to describe the genetic architecture of MS in other populations. The authors therefore argue that ancestral diversity is not merely a matter of equitable participant recruitment; it is an essential condition for producing accurate, generalizable and clinically useful knowledge about MS biology.
Genetics as a Framework for Interpreting Global Epidemiology
A globally representative map of MS susceptibility could help disentangle the genetic and environmental factors responsible for the striking geographical variation in disease prevalence. Age-standardized estimates cited in the article range from approximately 2 cases per 100,000 people in Oceania and 2.8 per 100,000 in central sub-Saharan Africa to 164.6 per 100,000 in high-income North America. These differences are influenced by unequal access to neurological services, magnetic resonance imaging, disease registries and standardized diagnostic procedures, but they may also reflect variation in allele frequencies, environmental exposures and gene–environment interactions. Migration studies offer a particularly informative natural experiment: individuals moving from regions of low MS prevalence to high-prevalence countries often experience increased risk, especially when migration occurs before adolescence. Such observations indicate that genetic susceptibility operates within environmentally sensitive developmental windows. A pan-ancestral genetic architecture, integrated with international epidemiological data, could therefore help estimate the “hidden burden” of MS in regions where cases remain undiagnosed and clarify whether population differences arise from biology, environmental exposure or deficiencies in health-care ascertainment.
The MHC as a Model of Ancestry-Dependent Genetic Architecture
The MHC region on chromosome 6 provides one of the strongest demonstrations of why ancestry-aware research is scientifically valuable. In European populations, HLA-DRB115:01 is the most prominent MS risk allele, but HLA allele frequencies and haplotype structures vary substantially across the world. The article’s global map illustrates that HLA-DRB115:01 is relatively common in Scandinavia, Central Europe and parts of North America, yet rare in Africa and South Asia. Other alleles that are uncommon or absent in European cohorts may be highly informative elsewhere. HLA-DRB104:05, for example, has been associated with MS in Japanese, Turkish, South American, African American and Sicilian populations, while HLA-DRB115:03 is particularly relevant in populations of African ancestry. These contrasts enable researchers to distinguish the effects of individual HLA alleles that are difficult to separate in European populations because they are inherited within long, highly correlated haplotypes. Studies of African American and Martinican cohorts helped demonstrate that the association attributed to the European DRB115:01–DQB106:02 haplotype is primarily driven by DRB1*15 alleles. Thus, ancestral variation functions as a natural experiment that can resolve immunogenetic mechanisms obscured within a single population.
Discovering Novel Loci and Identifying Causal Variants
Multi-ancestry genetics offers two complementary opportunities: the discovery of population-enriched risk variants and the refinement of established GWAS signals. The Sardinian TNFSF13B locus provides a compelling example. A deletion known as BAFF-var is relatively common in Sardinia but uncommon in mainland European populations, enabling its association with MS to be detected despite a comparatively modest sample size. Functional investigation showed that the variant creates an alternative polyadenylation signal, producing a shorter transcript lacking regulatory microRNA-binding sites. The resulting increase in soluble B-cell activating factor may promote B-cell survival, proliferation and immunoglobulin production, thereby facilitating loss of immune tolerance. This finding illustrates how a variant identified through the distinctive demographic history of one population can reveal a disease mechanism relevant to patients worldwide. Cross-ancestral fine mapping provides a second benefit. Because linkage disequilibrium blocks are generally shorter in populations of African ancestry, comparing association patterns across ancestries can reduce the number of variants considered plausible causal candidates. As illustrated in Figure 2 of the article, the lead GWAS variant may differ between European and African ancestry populations even when the same underlying causal variant is shared; integrating both association profiles narrows the genomic interval in which that causal variant is likely to reside.
Ancestry, Clinical Heterogeneity and Disease Severity
The article also considers whether genetic diversity might help explain variation in MS onset, progression and neurological disability. MS is clinically heterogeneous, yet susceptibility GWAS have so far explained little of the variance in relapse frequency, progression rate or treatment response. Epidemiological studies frequently report that African American and Hispanic American patients experience younger onset, greater disability at diagnosis, more rapid progression, increased inflammatory activity and higher mortality than white American patients. Nevertheless, such comparisons require careful interpretation because ancestry is correlated with social determinants of health, including delayed diagnosis, unequal access to specialist care, treatment disparities, socioeconomic disadvantage and clinician bias. The authors do not present genetics as an alternative to these structural explanations. Instead, they argue that adequately powered and carefully designed genetic studies could quantify how much phenotypic variation remains after environmental and social factors are considered. Extreme-phenotype designs may be particularly productive: comparing individuals with very benign disease against those with rapidly progressive or highly inflammatory MS could enrich for variants influencing severity rather than susceptibility. This approach may ultimately identify molecular pathways associated with neurodegeneration and disease progression, areas in which effective therapeutic targets remain urgently needed.
From Association Studies to Predictive and Causal Medicine
The translational importance of diverse GWAS extends beyond identifying susceptibility loci. GWAS summary statistics support polygenic risk scoring, Mendelian randomization, heritability estimation, genetic-correlation analysis, functional annotation and fine mapping. Polygenic risk scores aggregate the effects of numerous alleles to estimate an individual’s genetic predisposition and may eventually support early detection, clinical-trial stratification or targeted prevention. Their validity, however, depends on correspondence between the ancestry of the GWAS population used to derive the score and that of the patient in whom it is applied. Scores developed primarily from European datasets perform less accurately in non-European populations because allele frequencies, linkage disequilibrium patterns and estimated marginal effect sizes differ across ancestries. Although computational methods can partially improve portability, the article emphasizes that the greatest gains will require large, ancestry-specific GWAS. The same principle applies to Mendelian randomization, which uses genetic variants as instrumental variables to test whether epidemiological associations are likely to be causal. European-ancestry analyses have implicated childhood obesity and low vitamin D concentrations in MS risk, but equivalent datasets are required to determine whether these causal relationships are consistent across global populations. Without such evidence, precision medicine risks becoming precise only for groups already over-represented in research.
Building an Ethical and Scientifically Robust Global Research Programme
Achieving a global view of MS genetics will require more than simply adding diverse samples to existing analytical pipelines. Large sample sizes are necessary because most common MS risk variants have modest effect sizes, while the low diagnosed incidence of MS in some regions makes recruitment difficult. Investigators must also identify ancestry-matched controls, account rigorously for population stratification and use genotyping arrays or sequencing strategies that adequately capture variation outside European populations. Encouragingly, advances in local-ancestry inference, admixed-population GWAS, cross-ancestry genetic-correlation analysis and diverse reference panels are making these studies increasingly feasible. Equally important are research governance and community trust. Studies must be developed in sustained partnership with local investigators and participant communities, with benefits that include durable scientific infrastructure rather than extractive sample collection. Results must be communicated in ways that avoid racial essentialism, stigmatization and discrimination, particularly given the history of medical exploitation experienced by marginalized populations. Early and continuous participation by patients and researchers from the populations being studied is therefore both an ethical obligation and a prerequisite for scientific validity. The article concludes that consortium-scale, ancestrally inclusive research will deepen understanding of MS epidemiology, immunobiology and causal genetics while improving the fairness of genomic medicine for people with MS across 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.
