Uncovering the Genetic Drivers of Relapse-Independent Progression in Multiple Sclerosis
Multiple sclerosis is traditionally understood as an immune-mediated disease characterized by inflammatory relapses, demyelination, axonal injury, and progressive neurodegeneration. However, contemporary clinical research increasingly emphasizes that disability accumulation is not explained solely by relapses. A substantial proportion of patients experience worsening that occurs independently of acute inflammatory attacks, a phenomenon known as progression independent of relapse activity, or PIRA. The article by Clarelli and colleagues addresses this clinically important process by examining whether inherited genetic burden, summarized through polygenic risk scores, contributes to the rate of PIRA events in people with multiple sclerosis.
Why PIRA Matters Clinically
The concept of PIRA has reshaped the understanding of multiple sclerosis progression. Even when disease-modifying therapies successfully reduce relapse frequency, many patients continue to accumulate physical or cognitive disability over time. This silent progression may begin early in the disease course, including during the relapsing-remitting phase, and may represent a major driver of long-term disability. By focusing on PIRA rather than relapse-associated worsening, the study investigates a form of progression that remains insufficiently controlled by current anti-inflammatory therapeutic strategies and therefore represents a central challenge in modern multiple sclerosis care.
Polygenic Scores as Measures of Cumulative Genetic Burden
Polygenic risk scores are quantitative measures that aggregate the effects of many genetic variants across the genome. Instead of testing one genetic locus at a time, this approach estimates whether the combined burden of multiple variants is associated with a clinical phenotype. In this study, the authors used severity-related summary statistics from a large genome-wide association study of multiple sclerosis severity conducted by the International Multiple Sclerosis Genetics Consortium and the MultipleMS Consortium. The objective was not to predict susceptibility to multiple sclerosis, but rather to evaluate whether genetic liability linked to disease severity also influences relapse-independent disability progression.
Study Design and Patient Cohort
The investigators analyzed longitudinal data from 1162 Italian patients with multiple sclerosis followed at Ospedale San Raffaele and recorded in the Italian multiple sclerosis register. Patients with primary or secondary progressive disease at first neurological evaluation, clinically isolated syndrome, fewer than three EDSS assessments, follow-up shorter than five years, or participation in the original severity genome-wide association study were excluded. The final cohort had long clinical observation, with a median follow-up of 15.8 years. PIRA events were defined using confirmed EDSS worsening and were classified as relapse-independent when no relapse occurred from 90 days before to 30 days after the disability-worsening event.
Statistical Strategy and Main Findings
The authors calculated five polygenic scores at different p-value thresholds after clumping genetic variants to reduce linkage disequilibrium. They then tested associations between these scores and the number of PIRA events using negative binomial regression models, adjusting for sex, age at first EDSS evaluation, baseline EDSS, year of disease onset, follow-up duration, and ancestry-related principal components. In the overall cohort, the polygenic scores showed a consistent trend toward higher PIRA rates, but the associations did not reach nominal statistical significance. The most informative signal emerged when the analysis was restricted to patients with disease onset at or before 50 years of age, where the PRS calculated at the p < 0.05 threshold was significantly associated with PIRA rate.
Age at Onset as a Modifier of Genetic Effects
One of the most important observations in the study was the age-dependent nature of the genetic association. Among patients with age at onset ≤50 years, the PRS_P0.05 score was associated with a higher rate of PIRA events, and the association became stronger in the subset with age at onset ≤40 years. The authors also identified an interaction between polygenic score and age at onset, suggesting that the genetic contribution to PIRA becomes less pronounced as age at onset increases. This finding is biologically plausible, because late-onset disease may be more strongly influenced by aging-related mechanisms, comorbidities, and cumulative environmental exposures that can obscure or dilute the measurable effect of inherited genetic burden.
Scientific Significance and Future Directions
This study provides evidence that cumulative genetic load related to multiple sclerosis severity may contribute to relapse-independent disability progression, particularly in patients with earlier disease onset. Its findings support the view that PIRA is not merely a clinical consequence of aging or incomplete relapse recovery, but may partly reflect inherited biological mechanisms influencing neurodegeneration, repair capacity, or central nervous system resilience. Nevertheless, the study remains exploratory, and the reported associations require validation in independent cohorts with diverse ancestry backgrounds and harmonized longitudinal phenotyping. Future work integrating polygenic scores with imaging biomarkers, treatment exposure, environmental risk factors, and molecular profiling may help refine prognostic models and identify patients at higher risk of silent progression.
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:
Clarelli, F., Sorosina, M., Giordano, A., Mascia, E., Visentin, G., Missaglia, M., ... & Esposito, F. (2025). Contribution of Polygenic Scores to Progression Independent of Relapse Activity in Multiple Sclerosis. European journal of neurology, 32(7), e70264.
