The Enigma of MS Etiology: Find an Answer, Ask More Questions

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.