How Common is Multiple Sclerosis in Siblings?

This blog post seeks to answer the question, “How common is multiple sclerosis in siblings?” It summarizes the findings for associations between birth order and multiple sclerosis, the causes of the condition, and its statistics. The article also enumerates the risk factors and their management.

Multiple Sclerosis (MS) is a common debilitating neurological condition. It leads to damage of the myelin sheath, which covers the neurons and is implicated in neural communications. Therefore, MS leads to a problem in interactions between the central nervous system and the rest of the body.  

How Common is Multiple Sclerosis in Siblings?

Cullen O’Gorman and colleagues found that the risk of someone developing Multiple Sclerosis (MS) if their sibling has the condition is 1 in 37 (O’gorman et al., 2013). The recurrence risk for identical twins was 18% or 1 in 5, while that of non-identical twins was 1 in 22. 

The estimated risk for developing MS is much lower for individuals whose child or parent has MS. In the general population, the risk is 1 in 330.  

Birth Order and Multiple Sclerosis

A study conducted in 2005 by Dessa Sadovnick and other researchers investigated the association between birth order and MS. They obtained information from more than ten thousand individuals with MS and more than 25,000 unaffected siblings (Sadovnick et al., 2005). 

The researchers divided the participants into two groups, where one group contained siblings with one affected sibling and another with more than one sibling with MS. They reported the following results:

  • No association between birth order and the risk of developing multiple sclerosis;
  • Siblings with multiple sclerosis are usually younger than those without the disorder;
  • Later the child is born, the higher the risk of developing MS as groups with more than seven siblings from which one was affected, the sibling with MS was noted to have been born later. This finding was applicable to groups where more than one sibling had MS; and
  • No association between older siblings and a higher risk of MS, as suggested by previous findings. 

Causes of Multiple Sclerosis

  • Genetic Effects
  • Environmental Factors
  • Immunological Influences
  • Infectious Determinants
  • Other Speculations

Familial and Genetic Effects

It is established that MS is not a hereditary condition. However, the risk of developing the disorder may be determined by genetic factors. In 2005, Nete Munk Nielsen and colleagues investigated the familial risk of MS in a nationwide study  (Nielsen et al., 2005). 

They found that first-degree relatives are seven times at the risk of developing the disorder than the general population. These researchers also mentioned that MS patients’ spouses did not experience a higher risk of developing the condition, claiming a lack of a significant role of environmental influences in adults. 

A study conducted by researchers at the University of Illinois, Chicago, in 2015, identified a genetic variation known to occur two times more frequently in women than men. They studied five female siblings, out of which three had MS. The researchers found the genetic variation in all three of the affected siblings. 

Around a couple of hundred genes have a minor role in the risk of having the disorder. Research is still underway to understand genetic influences in MS better.

As noted earlier, the twin of an affected person is most susceptible to developing multiple sclerosis. If one twin has the disorder, the odds of the other developing MS is 1 in 5. The risk changes to 1 in 22 for non-identical twins.      

Environmental Factors

The following environmental factors may play a role in the development of MS.

Vitamin D

Low Vitamin D levels are thought to contribute to the development of MS. People living in areas closer to the equator receive more sunlight exposure, which is implicated in better immunity and consequent protection against immune-related disorders like MS.


Research postulated that obesity in childhood and teenage years is related to a higher risk of MS, and this finding is more so seen in women. Research has also shown an association between the risk of MS and obesity in adulthood. 


There are speculations regarding the influence of smoking on MS as smokers are at a twofold risk of developing MS than non-smokers. Smoking is also associated with higher severity and more rapid deterioration of the disease. 

Immunological Influences

People with MS have an atypical immune response, which leads to inflammation and impairment in the central nervous system. Various cells are implicated in this immune reaction, of which T cells and B cells are of primary significance. 

  • T cells are essential in the preparation and stimulation of B cells and other cells in the immune system to attack foreign bodies. In patients with MS, the T cells, upon activation in the lymph system, enter the CNS through blood vessels and cause inflammation and impairment by producing specific chemicals. Consequently, the myelin sheath is damaged, and those cells that manufacture myelin.
  • A type of T cells known as T regulatory cells helps minimize inflammation. In people with MS, these T regulatory cells are dysfunctional and do not reduce the inflammation effectively. 
  • After T cells activate B cells, the latter release antibodies and activate other proteins. However, in MS, such activation leads to CNS impairment.
  • Cytotoxic cells, also referred to as natural killer cells, attack and extinguish cells with specific features. Cytotoxic typically means toxic to cells. 

Infectious Determinants

Specific infectious agents, like measles, herpes virus-6, canine distemper, Chlamydia pneumonia, and Epstein-Barr virus (EBV), are hypothesized to increase the risk of developing MS. Research is still underway for these viruses and bacteria. 

The Epstein-Barr virus causes mononucleosis and has gained tremendous traction over a period for its role in MS. Research suggests that prior exposure to an infection due to EBV increases the odds of developing MS. 

Other Speculations

Other speculations include:

  • Organic or chemical solvents;
  • Exposure to hazardous materials, including heavy metals like mercury, manganese, and lead;
  • Environmental allergies; and
  • Exposure to domestic animals or pets

Risk Factors

Epidemiologists have outlined a few risk factors that make people more susceptible to developing the disorder, including:

  • Ethnicity
  • Location
  • Age 
  • Gender 


MS occurs typically in Caucasians of northern Europe. With that said, it is not that other ethnicities are free of risk. It is known to occur in almost every group, including Hispanic and African Americans. Different ethnic groups have different risk rates. African American women are thought to be at a higher risk than formerly believed. 


Multiple sclerosis is likely to increase in risk with an increase in distance from the equator. People closest to the equator are less likely to develop MS. However, the rates differ among groups within a specific location irrespective of where it is situated – closer to or farther away from the equator.


People diagnosed with MS typically lie between the ages of 20 and 50. However, this disorder can develop in younger children and older adults.


Women are more likely to develop the disorder than men, which indicates a hormonal influence on the risk factor.

Management of Risk Factors

You can manage your risk factors by doing the following things.

  • Maintain a healthy, well-balanced diet filled with fresh vegetables and fruits, nuts, whole grains and legumes, and lean protein. Processed foods, saturated fats, and refined sugars are likely to cause inflammation, and hence, need to be avoided. 
  • Exercise regularly. People are advised to engage in at least moderately intense workouts, such as walking, for two and a half hours in a week. 
  • Keep a handle on your weight.
  • Take vitamin D supplements if your blood levels are too low. Try to get exposure to sunlight as and when possible. 
  • Work on your stress levels by practicing mindfulness and relaxation techniques. Doing so will help minimize your body’s inflammation reaction.
  • Avoid smoking.


This blog post answered the question, “How common is multiple sclerosis in siblings?” It summarized the findings for associations between birth order and multiple sclerosis, the causes of the condition, and its statistics. The article also enumerates the risk factors and their management.

Frequently Asked Questions (FAQs): How Common Is Multiple Sclerosis in Siblings?

Is it common for siblings to have multiple sclerosis?

Yes, it is common for siblings to have multiple sclerosis. Identical twins are most susceptible, followed by non-identical twins, siblings, children, and parents.

Between men and women, who are more likely to develop MS?

Women are more likely than men to develop MS. They are at a two- or threefold risk of developing MS. 

Is multiple sclerosis a hereditary condition?

No, multiple sclerosis is not a hereditary condition. However, there is a genetic risk of developing the disorder. For example, a first-degree relative, like a sibling or a child, with MS increases your risk of having the condition. 

What are the familial risks of MS?

The familial risks of MS include the following: 
1 in 67 for a parent; 
1 in 48 for a child;
1 in 37 for a sibling;
1 in 22 for a non-identical twin; and
1 in 5 for an identical twin

Can stress result in multiple sclerosis?

There is no clear evidence to support the idea that stress results in multiple sclerosis. However, you may find it more challenging to deal with MS symptoms when you experience stress. Some people claim that stress played a role in triggering their symptoms or causing a relapse. 

What are the signs indicative of MS?

The following are signs indicative of MS.

Double vision;
Vision loss in one eye;
Paralysis of one side of the body;
Swallowing issues; and
Bladder- and bowel-related issues, usually that of control.

How does multiple sclerosis attacks include?

Multiple sclerosis attacks may include:

What are the types of MS?

Although there is no sure-fire way of saying how the condition will progress, there are four types of MS as defined by the International Advisory Committee on Clinical Trials of MS. These types include:

Clinically Isolated Syndrome
Relapsing Remitting
Secondary Progressive
Primary Progressive 


Multiple Sclerosis Trust. (2018, November). Risk of developing MS. Retrieved from,or%20sisters%20%2D%201%20in%2037.  

National Multiple Sclerosis Society. (n.d.). What Causes MS? Retrieved from  

National Multiple Sclerosis Society. (nd.d.). Who Gets MS? (Epidemiology). Retrieved from  

Nielsen, N. M., Westergaard, T., Rostgaard, K., Frisch, M., Hjalgrim, H., Wohlfahrt, J., Koch-Henriksen, N., & Melbye, M. (2005). Familial risk of multiple sclerosis: A nationwide cohort study. American Journal of Epidemiology, 162(8), 774–778.

O’gorman, C., Lin, R., Stankovich, J., & Broadley, S. A. (2013). Modelling Genetic Susceptibility to Multiple Sclerosis with Family Data. Neuroepidemiology, 40, 1–12.

Sadovnick, A. D., Yee, I. M. L., & Ebers, G. C. (2005). Multiple sclerosis and birth order: A longitudinal cohort study. Lancet Neurology, 4(10), 611–617.