Multiple Sclerosis
ICD-11: 8A40
Disease Overview
Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system, characterized by inflammation, demyelination, axonal damage, and progressive disability. Pathophysiology involves T-cell-mediated autoimmune attack on myelin and oligodendrocytes, with contributions from B cells, microglia, and innate immunity. Genetic susceptibility is substantial—twin concordance ~25%, SNP heritability ~0.25–0.30. The HLA-DRB1*15:01 allele is the strongest genetic risk factor, conferring ~3-fold increased risk. Non-HLA loci implicate immune regulation, vitamin D metabolism, and neuronal resilience. Environmental factors are critical: low vitamin D (from UV/sun exposure and diet), Epstein-Barr virus infection, and smoking amplify risk. Adolescence and young adulthood represent the peak period for disease onset—age 15–24 is when many individuals experience first symptoms. Vitamin D status and EBV seroconversion during this window may be particularly consequential for MS development.
MS commonly presents between ages 15–40; adolescent-onset MS may have distinct trajectory. Vitamin D deficiency and low sun exposure in youth are modifiable risk factors. EBV seroconversion timing (often in adolescence) influences MS risk. Smoking initiation in adolescence amplifies genetic susceptibility.
Genetic Architecture Summary
| Gene | Variant | GWAS p | Evidence | Strength |
|---|---|---|---|---|
| HLA-DRB1 | rs3135388 | 1.0e-50 | HLA-DRB1*15:01 is the dominant MS risk allele; antigen presentation and T-cell repertoire; strongest GWAS signal | 0.98 |
| CYP27B1 | rs703842 | 5.0e-9 | Vitamin D 1α-hydroxylase; converts 25-OH-D to active 1,25-(OH)2D; links UV/vitamin D to MS genetics | 0.82 |
| IL2RA | rs2104286 | 2.1e-8 | IL-2 receptor α; regulatory T-cell function; immune tolerance pathway | 0.78 |
PRS notes: PRS for MS achieve good discrimination (AUC ~0.72) due to strong HLA contribution. Vitamin D-G×E interactions documented but not in PRS. European-ancestry dominated; transferability limited.
Exposure Modifier Panel
| Exposure | Direction | Strength | Confidence | Mechanism hypothesis |
|---|---|---|---|---|
| diet-quality | buffer | 0.75 | HIGH | Vitamin D and omega-3 intake buffer MS risk; diet influences vitamin D status; CYP27B1 genotype may modify vitamin D responsiveness; low vitamin D amplifies risk |
| tobacco | amplify | 0.78 | HIGH | Smoking increases MS risk and accelerates disability; oxidative stress and immune modulation; G×E with HLA documented |
| air-pollution | amplify | 0.5 | MEDIUM | Particulate matter and traffic pollution may amplify neuroinflammation; oxidative stress; emerging epidemiological links |
Population Equity Notes
GWAS ancestry breakdown: MS GWAS overwhelmingly European-ancestry (>95%); disease prevalence and HLA associations differ by ancestry
Transferability notes: HLA-DRB1*15:01 association varies—strong in Northern European, weaker in Southern European, different alleles in African; non-HLA PRS transferability poor
Data gaps: Multi-ancestry MS GWAS; African and Latin American representation; G×E validation across populations
Tissue Context
Mechanism Brief Links
Visualizations
Risk Shift by Exposure Stratum
Population-level data only — does not predict individual risk
Tissue Relevance
References
- 1.International Multiple Sclerosis Genetics Consortium (2011). Genetic risk and a primary role for cell-mediated immune mechanisms in multiple sclerosis. Nature. doi:10.1038/nature10251
- 2.International Multiple Sclerosis Genetics Consortium (2019). Multiple sclerosis genomic map implicates peripheral immune cells and microglia in susceptibility. Science. doi:10.1126/science.aav7188
- 3.Pierrot-Deseilligny C, Souberbielle JC. (2017). Vitamin D and multiple sclerosis: an update. Multiple Sclerosis Journal. doi:10.1177/1352458517713386
- 4.Hedström AK, et al. (2016). Smoking and multiple sclerosis: evidence for gene-environment interaction. Neurology. doi:10.1212/WNL.0000000000002645
- 5.Lucas RM, et al. (2011). Sun exposure over the life course and associations with multiple sclerosis. Neurology. doi:10.1212/WNL.0b013e31822c7f45