The risk of developing multiple sclerosis is at least two to three times higher overall for women than for men, according to the National Multiple Sclerosis Society. Some estimates say the ratio may be more like 4 to 1 for women and men for certain types of MS.
The word “sclerosis” is defined as scarring. Multiple sclerosis is a condition that causes scar tissue to form on nerves due to damage in the brain, spinal cord, and optic nerves that carry images from the eyes to the brain.
Immune cells in the body normally fight off foreign invaders to prevent disease. MS causes the body’s immune cells to attack the fatty covering on nerves, which is call myelin.
Myelin acts like insulation on an electric cord. It protects the nerves and helps them send electric signals throughout the body. When myelin is damaged, scar tissue forms and the electric signals to and from the brain can be interrupted.
MS typically develops between the ages of 20 and 50. Researchers are uncertain as to why women are more likely to develop the disease than men, but research suggests that genetics, responses to the environment, and hormones may all play a role.
One study from the Washington University School of Medicine in St. Louis discovered a difference between the brains of men and women that may partially explain the gender bias.
Working first with mice then with mice and humans, these researchers tried to determine how immune cells that attack nerves were getting into the brains and spinal cords of people with MS.
Normally, the brain is protected by a tightly packed layer of cells known as the blood-brain barrier. The BBB allows nutrients and necessary substances to pass through, but blocks large molecules such as immune cells and viruses.
But in people with MS, immune cells get through the BBB and are able to damage nerves in the brain.
The Washington University researchers discovered that people with MS have more of a protein called S1PR2 in their brains. This protein relaxes the BBB and makes it easier for larger molecules to pass through that normally would have been blocked.
These researchers also recognized that among people with MS, women produce much more of the protein S1PR2 than men. This means the women’s immune cells have easier access to the brain and spinal cord where they do damage.
Another research study involving scientists from the Mayo Clinic, as well as experts from Northern Ireland, Belgium and Italy studied patterns in the genetic makeup of MS patients in several countries.
The international team noted that women with MS tend to have a genetic variation that causes them to produce high levels of a protein called interferon gamma. This protein is known to aggravate MS symptoms by causing inflammation and tissue damage.
The researchers noted that men who had the genetic variation related to interferon gamma were more likely to get MS than men without the variation. But the variation was less common among men than among women.
This might help explain why more women than men develop MS.
Scientist continue to look for both the cause of MS and the reason for the gender bias for women to develop the disease. Some cite a probable interaction between environmental and genetic factors in MS risks.(5)
One example is suspected differences in how men and women respond to sun exposure and vitamin D supplements. Some research suggests higher levels of vitamin D may help lower women’s risk for MS.(5)
Other research suggests differences in hormones between men and women may play a role. This idea is supported by MS changes documented in women during pregnancy. Research suggests that when estrogen and other hormone levels are higher, MS symptoms are reduced. (5)
Researchers continue to look for answers as to why MS is more common in women than in men. Further study involving men and women at multiple clinics in multiple locations around the world is needed to isolate genetic and environmental differences and to develop new treatment strategies.
If you have questions about MS or your genetic risks, talk to your health care provider.
Reviewed April 1, 2016
by Michele Blacksberg RN
Edited by Jody Smith