Researchers may have discovered a cause of multiple sclerosis

Researchers may have discovered a cause of multiple sclerosis

Multiple sclerosis (MS) is a condition that causes damage to the substance that covers nerve cells. This interrupts normal communication between nerves, leading to problems with movement, speech, and other functions. We don’t know what causes multiple sclerosis, but we think it is an autoimmune disease.

What is an autoimmune disease?

Autoimmune diseases develop when a person’s immune system goes after its own tissues and organs. Autoimmune disease can affect all parts of the body. For example:

–Type 1 diabetes. This is the type that usually affects kids and develops when abnormal antibodies attack certain cells in the pancreas, leaving it unable to produce enough insulin, so the body can’t regulate blood sugar properly

–Rheumatoid arthritis. Multiple joints and other organs become inflamed; the cause is unknown, but the presence of autoantibodies (antibodies directed against proteins in healthy tissues) and other abnormal immune function suggest it is an autoimmune disorder.

–Pernicious anemia. In this condition, anemia develops when the immune system produces antibodies that prevent absorption of vitamin B12 from food.

And these are just a few. Autoimmune conditions are especially scary because the immune system goes rogue for no apparent reason. These are favorite conditions of medical television and movies, such as “House,” “Grey’s Anatomy” and “The Big Sick.”

What triggers autoimmune diseases?

The most common explanation is that an affected person’s immune system, partly due to the genes they inherited, is primed to react abnormally to some trigger, such as an infection, an environmental exposure (like cigarette smoke), or some other factor. For most autoimmune diseases, we can’t easily figure out what triggers them. If we could, we might be able to prevent them.

Are there known triggers for MS?

Experts suspect a number of potential triggers or risk factors for MS. For example, some believe that it’s due to a chronic infection (although it’s unclear exactly which infection). Others believe that it’s primarily a genetic neurological disease. These theories challenge the idea that MS is truly an autoimmune disease.

Some studies suggest that head injuries might be a risk factor for MS. If true, it raises important questions about how MS develops and how it might be prevented. On the other hand, it’s not an easy thing to study because researchers would never intentionally cause head injuries to see if they cause MS. Another way to study this question is to enroll people who already have MS, look back at whether they had concussions, and then compare them with similar people who don’t have MS.

A study published in the September 2017 issue of Annals of Neurology did just that.

New research suggests that head trauma might trigger MS

This research included more than 7,000 people with MS and compared them with more than 70,000 people who were similar in other ways (including age, gender, and where they lived) but who did not have MS. Investigators looked for a history of physician-diagnosed concussion prior to age 20. It was important to determine whether any type of traumatic injury, or a concussion specifically, could be the link. So, researchers also assessed whether the study subjects had ever broken a bone in the upper or lower extremities prior to age 20.

Here’s what they found:

–Those who had suffered a single concussion between the ages of 10 and 20 had a 22 percent higher rate of MS than those who had never had a concussion.

–The rate of MS was more than doubled for those who had experienced more than one concussion.

–There was no connection between broken bones in the arms or legs and the risk of MS.

A study of this type cannot prove that a potential trigger (head injury) actually caused the condition of interest (MS). We can only say there is a possible link. But we do have data to suggest that there is a link, and likely not a link with other types of injuries. We might later learn that the connection isn’t between concussions and MS at all, but rather some other factor (such as a drug or other treatment) that is more common among those with head injuries.

Still, these findings are hard to ignore and could represent one more reason we should all be concerned about head injuries to the developing brain.

What’s next?

Additional studies are needed, both to replicate these findings and to figure out just how trauma can trigger an autoimmune disease. These studies can also provide clues as to whether trauma might trigger other autoimmune diseases as well. If we gain a better understanding of how autoimmune conditions develop and how to prevent them, these conditions could become a bit less scary.

(Robert H. Shmerling, M.D., is faculty editor of Harvard Health Publications.)