Multiple Sclerosis (MS) is an autoimmune disease where the body’s immune system mistakenly attacks the central nervous system, specifically the protective myelin sheath around nerve fibers in the brain and spinal cord. This damage disrupts nerve signal transmission, leading to a range of symptoms. While it is not considered an inherited disease in the same way conditions like cystic fibrosis or Huntington’s disease are, genetics do play a role in an individual’s susceptibility. The development of MS is a complex interplay between a person’s genetic makeup and various environmental factors.
The Genetic Link to Multiple Sclerosis
Multiple sclerosis is not transmitted directly from parent to child, yet a genetic predisposition significantly influences risk. This means that while no single gene causes MS, certain gene variations can increase the likelihood of developing the condition. Researchers have identified over 200 genes that each contribute a small amount to the overall risk. These genes often relate to the immune system’s function.
The risk of developing MS is higher for individuals with a family history of the disease compared to the general population, where the lifetime risk is approximately 1 in 330 to 1 in 1,000. For a first-degree relative, such as a parent, sibling, or child, the risk increases. A 2023 study found that people with a first-degree relative with MS were seven to eight times more likely to develop the condition. If a parent has MS, the risk for a child is about 1 in 50. For a sibling, the risk is approximately 1 in 20 to 1 in 37.
Identical twins, who share nearly identical genetic material, show a remarkably higher risk; if one identical twin has MS, the other’s risk is approximately 1 in 4 to 1 in 5, or about 25-31%. This still indicates that genetics are not the sole determinant, as not all identical twins develop the disease.
A notable genetic factor is the Human Leukocyte Antigen (HLA) gene complex, located on chromosome 6. Genes within this complex code for proteins involved in how the immune system recognizes foreign invaders. The variant HLA-DRB115:01 is consistently identified as the strongest genetic risk factor for MS across various populations, including Caucasian, Asian, and African-American groups. Individuals with one copy of this variant may have a roughly threefold increased risk, and those with two copies may have an eightfold increased risk.
Environmental and Lifestyle Risk Factors
Beyond genetic predisposition, environmental and lifestyle factors significantly influence MS development. These external elements are thought to interact with a person’s genetic susceptibility, potentially triggering the disease. For instance, a strong association exists between Epstein-Barr virus (EBV) infection and MS. EBV, which causes infectious mononucleosis, infects over 90% of the population, but specific aspects of its infection, such as high EBV-specific antibodies, are linked to an increased MS risk. Studies suggest that the risk of MS can increase significantly, possibly up to 32-fold, following EBV infection, particularly if it occurs in adolescence or later life.
Low levels of vitamin D are also consistently associated with a higher risk of MS. This link helps explain why MS is more common in regions further from the equator, where sunlight exposure and subsequent vitamin D production are lower. Observational studies have found that lower vitamin D levels, especially during childhood, may increase the likelihood of developing MS. For example, a meta-analysis showed that people with vitamin D deficiency had a 54% higher risk of MS than those with sufficient vitamin D status.
Lifestyle choices, such as smoking, also contribute to MS risk. People who smoke have a higher likelihood of developing relapsing-remitting MS compared to non-smokers, and smoking can lead to more relapses and worse progressive disease. Adolescent obesity is another recognized risk factor. Studies indicate that a high body-mass index (BMI) during childhood and adolescence is associated with increased MS development.
Assessing Individual Risk
Given the complex interplay of genetic and environmental factors, predicting who will develop MS is not straightforward. There is no single “MS gene” that guarantees disease development, making routine genetic testing for predicting MS currently unavailable and generally not recommended outside of research settings. While genetic testing can identify specific markers like HLA-DRB115:01 that raise risk, carrying these genes does not mean a person will certainly develop MS, as most individuals with these risk genes never do.
The risk of MS is multifactorial, meaning it arises from a combination of many genes, each with a small effect, alongside various environmental exposures. Having a relative with MS or carrying a known risk gene indicates a predisposition but does not determine an individual’s future.
Discussions about personal and family risk are best conducted with a healthcare provider or neurologist. These professionals can review a complete family and medical history, offering personalized context and guidance based on current scientific understanding. They can also discuss potential strategies to manage modifiable risk factors, such as maintaining healthy vitamin D levels or avoiding smoking, which may influence overall risk.