AAN: New answers to old questions about risk factors and disease modifiers

The precise causes of multiple sclerosis continue to baffle the scientific community, although in general most researchers agree that a combination of genes and environmental factors appear to play a role in influencing the risk of developing MS. In those people living with MS, there is a great deal of research ongoing that’s looking at different types of exposures that can impact the course of the disease, such as the rate of relapses, severity, and progression. At AAN, a handful of researchers took to the podium to present their latest findings about the genetic and environmental factors that affect the risk of MS and play a role in modifying disease course.

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To open the session, Drs. Kassandra Munger and Kathryn Fitzgerald (Harvard School of Public Health, USA) delivered back-to-back presentations on the relationship between dietary intake of sodium and MS risk, activity and progression. A number of pre-clinical studies in animals have suggested that sodium-rich diets may contribute to a worsening of MS-like symptoms. However, Dr. Fitzgerald’s analysis of 465 participants of the BENEFIT trial in which she measured sodium excretion in the urine showed that there was no association between sodium intake and disease course. Specifically, a high-sodium diet did not predict faster conversion from clinically isolated syndrome (CIS) to definite MS, nor was it associated with a change in new brain lesions, time to first relapse, or disability progression. Similarly, Dr. Munger’s analysis of 476 women living with MS from the Nurse’s Health Study showed that, overall, there was no association between sodium intake and risk of developing MS. These studies provide compelling, although not definitive, evidence that high sodium intake is not linked to MS.

In contrast to sodium intake, there is strong evidence to suggest that smoking tobacco can increase the risk of developing MS and may even accelerate disease progression. Dr. Navid Seraji-Bozorgzad (Wayne State University, USA) added another piece of evidence to the puzzle and presented data showing the effects of quitting smoking on brain shrinkage (which is associated with disease progression) in people living with MS. In his study of 254 participants with relapsing MS who had smoked cigarettes for over 5 years, he examined rates of brain volume loss in those who continued to smoke after beginning the study versus those who stopped smoking. Dr. Seraji-Bozorgzad found that in general, those who stopped smoking experienced a slower rate of brain shrinkage than those who did not, suggesting possible implications for slowing disease progression, although this wasn’t formerly tested. Dr. Seraji-Bozorgzad advised that, based on a strong body of evidence linking smoking and poor MS outcomes, quitting smoking should be counselled by medical practitioners to their patients living with MS.

There is increasing awareness that many people living with MS also live with multiple chronic medical conditions, called comorbidities, at a higher rate than the general population. These comorbidities can not only affect wellness and quality of life, but also interact with MS symptoms and influence disease course. Dr. Ruth Ann Marrie (University of Manitoba), who holds a Dr. Donald Paty Career Development Award from the MS Society, presented her findings on the association between physical comorbidities and psychiatric comorbidities in MS in a population-based study. Dr. Marrie used administrative health data from Alberta to identify 9,624 people with MS and 41,194 non-MS controls in her study. She found that in the MS population, hypertension, heart disease, lung disease, fibrymyalgia, and epilepsy were linked to an increased risk of depression; fibromyalgia, heart disease and lung disease were linked to anxiety disorders, while lung disease and inflammatory bowel disease were associated with bipolar disorder. These findings provide invaluable information for identifying specific treatment approaches and managing psychiatric comorbidities in people living with MS.

The human microbiome is a hot and evolving topic in MS research; while a great deal of attention is focused on the microbes living in the digestive system, some researchers have turned their focus towards examining microbes residing in the diseased brain. MS Society-funded researcher Dr. Christopher Power (University of Alberta) presented research investigating the abundance and composition of the brain microbiome in people living with MS. He found that both MS and non-MS brains exhibited evidence of microbe populations, although concentrations were significantly higher in regions of demyelination in the MS brain. What’s more, the genetic diversity of the bacterial colonies residing in these lesions was reduced relative to the brain overall. These findings point to the possibility that an imbalance in the composition of microbes living in the brain is associated with demyelination and neuroinflammation in people living with MS, although it is still unknown if this imbalance is a cause or consequence of the disease. Future studies will look to probing the functional significance of the brain microbiome in the context of health and disease, and determine whether targeting the brain microbiome is a viable approach to reducing the risk of MS and/or treating the disease.

If you have any questions or comments about the research about risk factors and disease modifiers presented at AAN, leave them below.

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