Is Multiple Sclerosis or MS Hereditary?
Multiple sclerosis (MS) affects close to 2.5 million people worldwide. Chances are, you or someone you know has been affected by this condition.
MS is a serious, debilitating disease that is mostly diagnosed from early to mid-adulthood. While treatment can relieve the worsening of symptoms, unfortunately, there is no cure yet. No one is sure what causes MS, but studies have shown that genetic, immunological, and environmental factors are involved.
So, Is Multiple Sclerosis Hereditary or Not?
The short answer is yes, MS is hereditary. Research has shown a strong association between genetic inheritance and MS.
Are you more likely to develop MS than the general population if a member of your family has MS? If so, is it purely due to genetics? Or do environmental factors also play a role?
To look for answers to these questions, researchers have used genetic epidemiological approaches—studies that recruit families (in which at least one individual of the family has MS) to research if heredity influences disease susceptibility.
A nationwide study published in 2005 included over 19,000 first-degree relatives (such as parents, children, and siblings) of Danish MS patients. Scientists found that first-degree relatives of MS patients had an increased risk of developing MS compared to the general population .
According to the National MS Society, 1 out of 750 people develop MS in the general US population. For anyone who has a first-degree relative with the condition, the risk increases to 1 out of 40. The risk may increase further for those who have more than one relative with the disease .
Is the risk of MS completely genetic? Maybe this higher "within-family-risk" is instead due to environmental factors. It is essential to consider researching factors outside of genetics, such as environmental elements, because family members living together are often exposed to similar environmental factors.
Researchers looked at people who live together and share the same family environment to investigate this question further. One variable in the study included individuals who were not biologically related, such as adopted siblings.
In a Canadian population-based study with a sample size of 15,000 MS patients, researchers found that the risk for non-biological relatives of an MS patient was not higher than that of the general Canadian population. However, the risk for a biological relative was significantly higher than that of the general Canadian population and non-biological relatives .
Genetic Factors Linked to MS
Scientists have consistently found that MS occurs more frequently within family members sharing genetic material with an MS patient. First-degree relatives such as parents, children, and siblings of MS patients develop the disease more often than distant relatives—the amount of genetic material you share is related to the risk of developing the disease. In other words, the more genes you share with an MS patient, the higher the risk of developing the disease. Therefore, there is a strong genetic component involved with MS.
HLA-DRB1 (official symbol) is part of a group of genes called the Human Leukocyte Antigen (HLA) complex. The HLA complex helps our immune system distinguish the body’s proteins from those made by foreign invaders (such as microbes). Because of the critical role these genes play in the immune system, changes in them might be linked to damage of the myelin sheath and nerve cells as a result of an autoimmune response.
HLA-DRB1 changes have been reported as one of the strongest genetic risk factors for developing MS. Many other gene variants that are implicated in the risk for MS have been spotted. These include CYP27B1, HLA-DRB1, IL2RA, IL7R, and TNFRSF1A.
Environmental Factors Linked to MS
There have been considerable arguments over the years as to whether environmental factors rather than genetic factors can be associated with MS. It has become apparent that both environmental and genetic factors correspond with MS, and that they may interact with each other.
Even though the cause of MS is unknown, studies on twins have shed some light on the factors that may be involved. Identical twins share 100% of their genetic material. Hence, if one twin has MS, one would expect the risk for the other to have MS to be 100%; however, this is not the case. In fact, the chance of one twin having MS (if the other has the disease) is about 31% . The fact that identical twins do not have a substantial risk of sharing the condition suggests that MS is not an entirely genetic disease and that other factors must contribute.
Some environmental risk factors that may be potential triggers for MS are an Epstein-Barr virus infection, vitamin D or sunlight deficiency, and smoking.
- Epstein-Barr virus (EBV) infection: EBV is a herpes virus that is known to cause several medical conditions. Scientists believe that EBV is a large contributor to MS risk. Those infected with EBV have an increased risk of MS developing by more than three folds.
- Sunlight and vitamin D deficiency: Strong evidence has been found implicating vitamin D and sunlight deficiency in MS susceptibility. MS becomes more common as you move away from the equator (review map above). That is, the more sunshine a region receives, the lesser its frequency of MS. Sunlight is our main source of vitamin D. A study was conducted within the US military in which researchers obtained samples from military members prior to the members developing MS. Vitamin D levels in those samples were measured. Deficiency in vitamin D was found to be accompanied by a high risk of developing MS.
- Smoking: We all know that smoking is bad for several reasons. It turns out smoking is debilitating for people with MS. An interesting study has found that MS progression is more likely to occur in smokers. The smoking patterns of patients with MS were analyzed together with the way their disease progressed. The disease progression after the onset of MS was found to increase with the degree of smoking.
MS is referred to as a complex disease because it is associated with several risk factors. Therefore, MS is probably an element of chance. Is MS genetic? It can be said that both genetic and non-genetic factors are involved in MS.
Professor Anne-Louise Ponsonby on the Triggers for Multiple Sclerosis
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Do you know a family where more than one person has MS?
- Nielsen et al. (2005) "Familial Risk of Multiple Sclerosis." American Journal of Epidemiology. Vol. 162, No. 8
- "What Causes MS", National Multiple Sclerosis Society
- G.C. Ebers, A.D. Sadovnick, N. J. Risch. (1995). "A Genetic Basis for Familial Aggregation in Multiple Sclerosis". Nature. 377(6545): 150-1
- Balnyte et al. (2013)
- "A population-based study of multiple sclerosis in twins: update." Sadovnick et al. (1993).