SUMMARY

• c A study of more than 2,000 people with MS in Sweden suggests that people who had occupational exposure to organic solvents and certain MS susceptibility genes were much more likely to develop MS than those without MS genes.
• c In addition, they found significant additive effects such that having MS genes along with exposure to solvents and cigarette smoking created a 30-fold increased risk of developing MS.
• c “Avoidance of cigarette smoke and unnecessary exposure to organic solvents, particularly in combination, would appear reasonable lifestyle modifications to reduce the risk of MS, especially in those with a family history of the disease,” notes an accompanying editorial.
• c It’s important to note that many people have MS risk factors and will never develop MS, and many people develop MS without having been exposed to identified risk factors. Understanding what causes MS will speed the process of finding more effective ways to treat it and – ultimately – cure it, or even prevent it from occurring in the first place.
• c Anna Karin Hedström, MD, PhD, and colleagues (Karolinska Institute, Stockholm) report the study in Neurology. The study was funded by the Swedish Medical Research Council, Swedish Research Council for Health, and other supporters.

DETAILS

Background: MS is thought to occur when people whose genes make them susceptible encounter something in their environment that triggers this immune-based neurological disease. Some factors found to increase the risk of getting MS include cigarette smoking, adolescent obesity, vitamin D deficiency and Epstein-Barr virus infection. Genes that have been shown to affect MS susceptibility include HLA genes, which control how the immune system identifies targets for destruction.

Solvents are substances that are capable of dissolving or dispersing one or more other substances. Organic solvents contain carbon in their molecular structure and are used in such products as paints, varnishes, lacquers, adhesives, glues, and degreasing/cleaning agents, and in the production of dyes, polymers, plastics, textiles, printing inks, agricultural products, and pharmaceuticals. A 2012 review of the medical literature noted that organic solvents may be a risk factor for MS and other diseases.

Many people have MS risk factors and will never develop MS, and many people develop MS without having been exposed to identified risk factors. Understanding what causes MS will speed the process of finding more effective ways to treat it and – ultimately – cure it, or even prevent it from occurring in the first place.

This Study: Researchers recruited 2,042 people who had recently been diagnosed with MS in Sweden, and 2,947 people without MS. Blood tests were used to determine whether the participants had the HLA-DR15 gene, which is associated with an increased risk of developing MS, or lacked the HLA-A02 gene, associated with protecting against MS.

Researchers collected information on environmental exposures and lifestyle factors using a standardized questionnaire. Participants reported whether they had been occupationally (in the workplace) exposed to organic solvents, painting products, and/or varnish. Information also was collected on current and previous smoking habits.

Results: MS risk increased significantly in people with occupational exposure to organic solvents compared with people with no exposure. (Specific products or types of solvents were not identified.) People who had both MS risk genes and exposure to solvents were nearly seven times as likely to develop MS as people without MS genes and solvent exposure. People who had been smokers, in addition to having the genes and solvent exposure, were 30 times more likely to develop MS than those who have never smoked or been exposed to solvents and did not have the MS genes.

Anna Karin Hedström, MD, PhD, and colleagues (Karolinska Institute, Stockholm) report the study in Neurology (published online July 3, 2018). The study was funded by the Swedish Medical Research Council, Swedish Research Council for Health, Working Life and Welfare, Knut and Alice Wallenberg Foundation, AFA Insurance, Swedish Brain Foundation and Neuro Sweden.

Comment: This study suggests that environmental factors and MS susceptibility genes may interact and exponentially increase MS risk far beyond the individual factors alone. Further research is necessary to determine the underpinnings of this association. The authors suggest that inflammation caused by smoking and organic solvents in the lungs may heighten the inflammatory effects of MS genes.

“Future work identifying the specific causal organic solvents, along with their precise influence on immunologic function… is urgently needed,” comment Jack S. Bell, BM, BCh, and Gabriele C. DeLuca, MD, DPhil (John Radcliffe Hospital, Oxford, UK) in an accompanying editorial. “In the meantime, avoidance of cigarette smoke and unnecessary exposure to organic solvents, particularly in combination, would appear reasonable lifestyle modifications to reduce the risk of MS, especially in those with a family history of the disease.”

It’s important to note that participants in the study who were exposed to organic solvents were exposed through the workplace. Other exposures are usually much lower and of a shorter duration. Workplace risks can be minimized.