Polygenic Risk Scores Reveal Genetic Stratification of Lifetime Multiple Sclerosis Risk
Multiple sclerosis (MS) is a chronic autoimmune neurological disorder characterized by inflammation, demyelination, and progressive neurodegeneration in the central nervous system. Although environmental factors such as viral infections, smoking, and vitamin D deficiency contribute to disease susceptibility, genetic predisposition plays a substantial role in MS risk. Over the past decade, genome-wide association studies (GWAS) have identified more than 200 genetic loci associated with MS susceptibility. However, understanding how these genetic variants collectively influence an individual’s lifetime probability of developing MS remains a significant challenge. The study by Loonstra et al. (2024) addresses this gap by examining how polygenic risk scores (PRS) correlate with lifetime disease risk within a well-defined population cohort.
Study Design and Population-Based Cohort
The investigators conducted a population-based analysis using participants from the Project Y cohort, which includes individuals born in the Netherlands around 1966. This unique design allowed the researchers to identify nearly all individuals diagnosed with MS from this birth year, providing a rare opportunity to examine lifetime risk in a near-complete population sample. The study included 285 individuals with MS and 267 control participants without MS, drawn from both the Project Y cohort and the Amsterdam Dementia Cohort. Genetic data were generated through genotyping and imputation techniques, enabling the researchers to analyze known MS-associated variants across the genome.
Construction of the Polygenic Risk Score
A polygenic risk score aggregates the effects of many genetic variants into a single quantitative measure representing inherited susceptibility to a disease. In this study, the PRS was calculated using variants and effect sizes derived from the largest available MS genetic association studies. Each participant received a PRS reflecting the cumulative impact of hundreds of susceptibility loci. To interpret the distribution of genetic risk across the population, individuals were categorized into deciles based on PRS values, using the distribution observed in the control population. This approach enabled the researchers to compare lifetime MS risk across progressively higher levels of genetic predisposition.
Genetic Risk and Lifetime Probability of MS
The analysis revealed a clear gradient between polygenic risk score and lifetime probability of developing MS. Individuals with higher PRS values exhibited a substantially elevated risk compared with those in the lowest risk categories. Notably, women in the lowest 30% of genetic risk had an estimated lifetime MS occurrence of approximately 1 in 2,739, whereas women within the top 10% of genetic risk had a markedly higher probability of developing the disease. These findings demonstrate that cumulative genetic burden significantly influences lifetime MS susceptibility, even though MS remains a relatively rare condition overall.
Sex Differences in Genetic Risk
An important observation from the study is the pronounced sex difference in MS risk. Multiple sclerosis occurs more frequently in women than in men, a pattern that is also reflected in genetic risk estimates. The PRS-based lifetime risk calculations showed stronger absolute risk differences among women across genetic risk strata. This suggests that while the same genetic variants may contribute to susceptibility in both sexes, the overall risk landscape is modulated by sex-related biological factors, potentially including hormonal influences and immune regulation differences. These results reinforce the importance of considering sex as a critical variable in genetic risk modeling.
Relationship Between Polygenic Risk and Disease Course
Beyond susceptibility, the study also explored whether polygenic risk scores correlate with disease progression characteristics. Specifically, the researchers examined associations between PRS and variables such as age at disease onset and time to secondary progressive MS, a stage characterized by gradual neurological decline. The analysis did not demonstrate strong associations between PRS and these disease progression markers. This finding suggests that while genetic susceptibility loci are important for initiating disease risk, other biological mechanisms or environmental exposures may play a larger role in determining how the disease progresses after onset.
Implications for Precision Medicine and Risk Prediction
The findings from this population-based study highlight the potential utility of polygenic risk scores for estimating individual susceptibility to complex diseases like multiple sclerosis. While PRS alone is not sufficient for clinical diagnosis or screening, integrating genetic risk with environmental and lifestyle factors could improve predictive models in the future. Such approaches may ultimately enable earlier identification of individuals at higher risk, opening the door for targeted prevention strategies or monitoring programs. Nevertheless, ethical considerations, population diversity, and predictive accuracy must be addressed before PRS can be widely implemented in clinical practice.
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:
Loonstra, F. C., Álvarez Sirvent, D., Tesi, N., Holstege, H., Strijbis, E. M., Salazar, A. N., ... & Uitdehaag, B. (2024). Association of polygenic risk score with lifetime risk of developing multiple sclerosis in a population-based birth-year cohort. Neurology, 103(7), e209663.
