The research, led by Anna Karin Hedström, Tomas Olsson, and Lars Alfredsson of Karolinska Institutet and published in the Journal of Neurology, drew on the Epidemiologic Investigation of Multiple Sclerosis, a population-based study that recruited newly diagnosed patients from 40 neurology units across Sweden, including every university hospital, between April 2005 and December 2021. Of 3,792 incident cases enrolled with a participation rate of 91 percent, the final analytic sample comprised 3,094 individuals after excluding those with uncertain family history or missing follow-up disability data. Each participant completed a structured questionnaire at inclusion covering demographics, environmental exposures, lifestyle factors, and family history of the disease.

Participants were sorted into three groups based on their closest affected relative: those with no known family history, those with a first-degree relative with multiple sclerosis, and those with a second- or third-degree relative with the disease. In total, 239 participants, or 7.7 percent, reported an affected first-degree relative, while 468, or 15.1 percent, reported an affected second- or third-degree relative. This hierarchical classification by degree of relatedness is a methodological strength, because many earlier studies lumped all familial cases together or relied on small clinic-based samples that could not disentangle the effects of relatedness from other prognostic factors.

The study then linked participants to the Swedish MS Registry, a nationwide resource integrated into routine clinical practice in which neurologists prospectively record disease activity, neurological function, and treatment exposure at every visit. Baseline was defined as the first available Expanded Disability Status Scale assessment, and the primary outcome was confirmed disability worsening, defined as a sustained increase of at least 1.0 EDSS point confirmed at a subsequent visit at least six months later, with adjustments for lower baseline scores. The researchers also tracked time to EDSS milestones 3 and 4, new or enlarging T2 lesions on MRI, cognitive decline on the Symbol Digit Modalities Test, and worsening on the patient-reported Multiple Sclerosis Impact Scale-29, capturing both physical and psychological dimensions of the disease.

Using Cox proportional hazards regression adjusted for age, sex, ancestry, education, calendar year of diagnosis, disease duration, baseline disability, smoking, body mass index, and initial disease-modifying therapy, the team found no significant associations between family history status and any of these outcomes. The hazard ratio for confirmed disability worsening was 1.06 among people with a first-degree relative with the disease and 1.04 among those with a second- or third-degree relative, with confidence intervals spanning unity in both cases. Separate analyses of relapse-associated worsening and progression independent of relapse activity, the two components of confirmed worsening, likewise showed no clear differences, and sensitivity analyses that modeled treatment as a time-varying covariate or reclassified participants with uncertain family history left the conclusions unchanged.

The negative findings extended across every domain examined. MRI disease activity, measured as the first appearance of new or enlarging T2 lesions, showed hazard ratios of 1.11 and 0.95 for the first-degree and second-/third-degree groups respectively. Cognitive worsening, defined as a drop of eight or more points on the Symbol Digit Modalities Test, yielded hazard ratios of 1.05 and 0.93, and a stricter four-point threshold produced similar results. Patient-reported worsening on both the physical and psychological subscales of the MSIS-29 was also unrelated to family history. Linear mixed-effects models tracking longitudinal change over time found no evidence that trajectories differed among the family history groups for cognition or for either patient-reported subscale, with interaction p-values ranging from 0.267 to 0.941.

One baseline difference did emerge: individuals with a first-degree relative with multiple sclerosis were significantly more likely to carry the HLA–DRB1*15:01 allele, the strongest genetic risk factor for the disease, with 68.3 percent positivity compared with 52.8 and 53.4 percent in the other groups. Beyond this, however, the groups were remarkably similar at disease onset. Age at onset, sex distribution, disease phenotype, smoking habits, body mass index, sun exposure, physical activity, Epstein-Barr virus antibody levels measured against the main MS-associated EBNA-1 peptide segment, and vitamin D levels showed no meaningful differences, suggesting that people with and without familial disease constitute clinically and epidemiologically comparable populations once the disease has declared itself.

The authors argue that this overall similarity points to a fundamental biological distinction between disease initiation and disease progression. Most of the more than 200 genetic susceptibility loci identified through genome-wide association studies relate to immune regulation and the risk of developing multiple sclerosis in the first place, not to how severe the disease becomes afterward. Familial clustering, on this view, primarily reflects shared predisposition to disease onset, while later progression is driven by other forces, including treatment exposure, aging, comorbidities, and lifestyle factors. A recent genome-wide association study published in Nature identified a severity locus implicating central nervous system resilience, underscoring that the genetics of progression may be largely separate from the genetics of susceptibility.

The researchers also acknowledge that family history is a blunt instrument. It does not capture the underlying burden or composition of genetic risk variants, and it conflates inherited factors with shared familial environment. Individuals classified as having familial disease may carry very different genetic risk profiles, while some people without a known affected relative may nonetheless harbor substantial inherited susceptibility. Such heterogeneity would tend to dilute any true association toward the null. Self-reported family history may also be incomplete, particularly for more distant relatives, introducing nondifferential misclassification. Yet the absence of any consistent gradient across degrees of relatedness in the sensitivity analyses argues against a hidden signal of clinically meaningful magnitude.

For patients and clinicians, the practical message is considerable. A family history of multiple sclerosis, which often looms large in the minds of newly diagnosed patients and their relatives, should not by itself be treated as a marker of worse prognosis or a reason to escalate therapy more aggressively. The study does not rule out modest effects, particularly among the comparatively small first-degree group, and the observational design leaves open the possibility of residual confounding by treatment decisions or unmeasured factors such as depression. But within the limits of a nationwide cohort with long-term follow-up, the conclusion is clear: inherited susceptibility shapes who develops multiple sclerosis, not how the disease unfolds once it has begun. The search for the determinants of progression must therefore look elsewhere, toward the emerging genetics of severity and the modifiable exposures that follow diagnosis.

Subject of Research: The prognostic impact of family history of multiple sclerosis on long-term disease outcomes

Article Title: Family history of multiple sclerosis and long-term outcomes

Article References: Hedström, A. K., Olsson, T., & Alfredsson, L. (2026). Family history of multiple sclerosis and long-term outcomes. Journal of Neurology, 273(10), Article 622. https://doi.org/10.1007/s00415-026-14162-9

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14162-9

Keywords: multiple sclerosis, family history, disability progression, HLA-DRB1*15:01, genetic susceptibility, prognosis, MRI disease activity, cognitive decline, Swedish MS Registry, EIMS, relapsing-onset MS, epidemiology