Simpson, Jr. SL, Greenhill K, van der Mei I, Stankovich J, Charlesworth J, Taylor B. “The varied mechanisms of vitamin D in the onset and clinical course of MS: potential roles in modulating other aetiologic pathways.” Current Medical Literature – Neurology. 2011; 27(1): 1- 14. [ERA 2010: NR]
Chapter 5:
Simpson Jr. SL, Taylor B, Blizzard L, Ponsonby A-L, Pittas F, Tremlett H, Dwyer T, Gies P, van der Mei I. “Higher 25-hydroxyvitamin D is associated with lower relapse risk in MS.” Annals of Neurology. Aug 2010; 68(2): 193-203. [ERA 2010: A*]
Chapter 6:
Simpson Jr. SL & Stewart N, van der Mei I, Eyles D, Ko P, Ponsonby A-L, Pittas F, Blizzard L, Dwyer T, Taylor B. “Interferon-β is associated with higher serum 25-hydroxyvitamin D and both interact to modulate relapse risk in multiple sclerosis .” Neurology. In-press (Accepted 15 November 2011). [ERA 2010: A]
Chapter 7:
Simpson, Jr. SL, Taylor B, Dwyer D, Taylor J, Blizzard L, Ponsonby A-L, Pittas F, Dwyer T, van der Mei, I. “Anti-HHV-6 IgG titers are significantly predictive of relapse risk in multiple sclerosis.” Multiple Sclerosis. doi: 10.1177/1352458511428081. [ERA 2010: A]
Other publications
van der Mei I, Simpson, Jr. SL, Stankovich J, Taylor B. “Individual and joint action of environmental factors and risk of MS”, Neurologic Clinics. May 2011; 29; 233 – 255. [ERA 2010: NR]
van der Mei, I, Simpson, Jr. SL, Knippenberg S, Winzenberg T, Taylor BV. “The role of vitamin D in multiple sclerosis: implications for disease management” Neurodegenerative Disease Management (Invited review). 1(6); 523-36. [ERA 2010: NR]
Conference presentations arising from work in this thesis
Oral presentations
2009 “Increasing levels of vitamin D are associated with decreased hazard of relapse in multiple sclerosis”, 2009 Australian and New Zealand Association of Neurologists Annual Scientific Meeting, Christchurch, NZ, 17-21 May 2009.
“The epidemiology of multiple sclerosis in Greater Hobart, Tasmania: 1951-2009”, Multiple Sclerosis Research Association Progress in MS Research Scientific Conference, Sydney, 14-17 Oct 2009. 2010 “Latitude is positively associated with the prevalence of multiple sclerosis: a definitive
demonstration of the latitudinal gradient hypothesis using meta-analysis”, Australasian Epidemiological Association Annual Meeting, Sydney, 29 Sept-1 Oct 2010.
“The role of human herpesvirus 6 in the clinical course of multiple sclerosis”, 2010 Student Excellent in Research Conference, Hobart 16-17 Nov 2010.
2011 “Anti-HHV IgG and clinical outcomes in multiple sclerosis”, 2011 Australian and New Zealand Association of Neurologists Annual Scientific Meeting, Hobart, 16-19 May 2011.
“Interferon-β is associated with higher 25-hydroxyvitamin D and both interact to modulate relapse risk in multiple sclerosis”, Multiple Sclerosis Research Association Progress in MS Research Conference, Melbourne, 26-28 Oct 2011.
Poster presentations
2009 “The epidemiology of multiple sclerosis in Greater Hobart, Tasmania: 1951-2009”, 2009 Australian and New Zealand Association of Neurologists Annual Scientific Meeting, Christchurch, NZ, 17-21 May 2009.
“Increasing levels of vitamin D are associated with decreased hazard of relapse in multiple sclerosis”, Multiple Sclerosis Research Association Progress in MS Research Scientific Conference, Sydney, 14-17 Oct 2009.
Awards received from the work described in this thesis
Young Investigator Award for best oral presentation at the Multiple Sclerosis Research Association Progress in MS Research Conference, Melbourne, 26-28 Oct 2011.
List of abbreviations
Abbreviation Full term
μg Micrograms
1,25(OH)2D 1,25-dihydroxyvitamin D
25(OH)D 25-hydroxyvitamin D
95% CI 95 percent Confidence Interval
ABS Australian Bureau of Statistics
AHR Adjusted Hazard Ratio
APC Antigen Presenting Cell
BMI Body Mass Index
CNS Central Nervous System
CSF Cerebrospinal fluid
DIS Dissemination in space
DIT Dissemination in time
EBNA Epstein-Barr Nuclear Antigen
EBV Epstein-Barr Virus
EBV-EA Epstein-Barr Virus Early Antigen
EDSS Kurtzke Expanded Disability Severity Scale
EIA Enzyme-linked Immunoassay
ELISA Enzyme-linked Immunosorbent Assay
HERV Human Endogenous Retrovirus
HHV Human Herpesvirus
HHV-6 Human Herpesvirus 6
HLA Human Leukocyte Antigen
HLA-DRB1 Most prevalent beta-subunit for Class II Major Histocompatibility
Complex
HR Hazard Ratio
IFA Immunofluorescence Assay
IFN-β Interferon beta
IgG Immunoglobulin class G
IgM Immunoglobulin class M
IL Interleukin
IQR Interquartile Range
ISR Incidence Sex Ratio
IU International Units
Km Kilometers
MET Metabolic Equivalent of Task
MRI Magnetic Resonance Imaging
MS Multiple Sclerosis
MSFC Multiple Sclerosis Functional Composite
MSL Multiple Sclerosis Longitudinal Study
MSSS Multiple Sclerosis Severity Score
nmol/L Nanomoles per Liter
NSW New South Wales
PBMC Peripheral Blood Monocyte
PCR Polymerase Chain Reaction
RRMS Relapsing-Remitting Multiple Sclerosis
RTI Respiratory Tract Infection
SD Standard Deviation
SED Standard Erythemal Dose
SPMS Secondary-Progressive Multiple Sclerosis
TAS Tasmania
Th1 Helper T-lymphocyte class 1
Th2 Helper T-lymphocyte class 2
Th17 Helper T-lymphocyte class 17
Treg Regulatory T-lymphocyte
WA (Australia) Western Australia
UK United Kingdom of Great Britain and Northern Ireland
USA United States of America
UVR Ultraviolet radiation
VCA Epstein-Barr Virus Viral Capsid Antigen
VDBP Vitamin D binding protein
VDR Vitamin D receptor
VDRE Vitamin D receptor element
Chapter 1. Background on multiple sclerosis, its history, pathophysiology,
diagnosis and treatment
1.1 Introduction
Multiple sclerosis (MS) is a chronic inflammatory autoimmune condition of the central nervous system (CNS), manifesting in alterations in and/or loss of neurological function, including sensory, motor and cognitive. The causes of MS are complex, and the exact causes of the disease and drivers of its clinical course remain unclear. Keys to teasing out the causal mechanisms of the disease, however, may be found via epidemiological research, interpreting biological specimens, environmental exposures and behaviour to find associations with disease occurrence and clinical course.
The research presented in this thesis is the result of such epidemiological research: the first two analyses examine the local and global distribution of MS occurrence, the interpretation of which may glean prediction of the temporal and spatial dynamics of disease; the subsequent analyses evaluate environmental and infectious determinants of clinical course, which help understand some of the underlying pathology and may be of use in development of diagnostic and treatment applications in MS.
While the work presented herein is epidemiological, with no pathological, immunological or biomolecular analyses having been undertaken, a brief discussion of these aspects, along with a summary of the history and current medical knowledge about MS, is necessary for context. In addition will be presented information specific to the subject areas discussed in analyses included in this thesis, including the epidemiology of MS in Greater Hobart and the distribution of MS globally, the role of vitamin D in MS onset and clinical course, and the role of human herpesviruses, particularly Epstein-Barr virus and human herpesvirus 6 in MS onset and clinical course.
1.2 The history of MS
Like many diseases of middle age, MS didn’t reach notice until relatively recently in history. In contrast to the multivariate infectious ailments which felled most people before they reached their fourth decade of life, MS would have been sufficiently rare as to not rise to the attention of the amateur researchers and physicians of history and, where it was noticed likely attributed to any number of spiritual or otherwise incorporeal causes. Thus, though it has likely existed for as long as humans achieved sufficient population density as to allow co-evolution of the variety of infectious pathogens and commensals as exist today, it is only in the last several hundred years that it was recognised, and only in the mid-19th century that it was identified as a distinct condition.
The earliest record of an ailment suggestive of MS is recounted in the Saga of Bishop Thorlak, the patron saint of Iceland and Bishop of Iceland from 1178 to 1193, concerning a woman named Halldora(1). The story tells that the Bishop was able to cure Halldora, this cited as one of the miracles for which he was later beatified, though the description of Halldora’s condition is perhaps more illuminating, for its similarity to progressive MS, sans the miraculous treatment:
(1)
A case description which is often cited as possibly being MS is that of Lidwina of Scheidam, in the Netherlands, in the late 14th century(2). This devout woman, subsequently beatified, developed progressive disability in her teens before passing away at 37 years of age. More recent to this is the case
of Margaret Davis in the late 17th century, who had progressive ‘lameness’ for several years following a peripartum illness, progressing to her becoming bedridden and finally expiring. As described by Gough:
(3)
More recent still, and of great utility for its detail, is the case of Augustus d’Este who, following a loss of vision after the funeral of a friend in 1822, kept a diary of his illness for two decades. His initial loss of vision and subsequent recovery shortly thereafter, as well as a recurrence of the loss of vision alongside sensations of pain throughout his body, and later a total numbness and loss of function in his legs, are highly reminiscent of relapsing-remitting MS(2, 4). This latter episode is strikingly described by d’Este:
The first mention of a case of MS in medical literature comes in 1824, by Charles Prosper Ollivier d’Angers in his “Traité des maladies de la moelle épinière”, with the description of a patient in his 20s who developed weakness at 17, progressing to his requring a cane to walk(2, 5). The first illustrative depictions of MS pathology were done by Robert Carswell in 1822(2), published amidst a number of illustrations of neurological pathologies he drew for a medical atlas. The first (Figure 1.1), what Carswell attributed to ”cartilaginous transformation of the spinal arachnoid of old persons”, is strongly suggestive of demyelinated lesions throughout the spinal cord(6). The second (Figure 1.2), which Carswell called “a peculiar disease state of the chord and pons Varolii, accompanied with atrophy of the discoloured portions”, is today regarded as a classical depiction of MS and is frequently cited as the first such illustration(6).
Figure 1.1. Depiction of spinal cord
abnormality likely to be MS, by Carswell. Figure 1.2. Depiction of spinal cord and pons abnormalities likely to be MS, by Carswell.
Figures reproduced from Carswell 1838(6) In parallel with the work by Carswell, however, Jean Cruveilhier was developing a series of pathology lithographs (Figure 1.3, Figure 1.4). Indeed, it was Cruveilhier’s work which was cited by Charcot in his later work (see below), though historical credit for the first illustrations of MS pathology goes to Carswell(2)
Figure 1.3. Lithograph of CNS abnormalities likely to be MS, by Cruveilhier
Figure 1.4. Lithograph of CNS abnormalities likely to be MS, by Cruveilhier
Figures reproduced from Cruveilhier 1835(7)
These historical instances of MS are retrospectively diagnosed today, but the first instances of disease being diagnosed as a discrete condition came in the mid-19th century. In much the same fashion as Carswell and Cruveilhier, characterisation of the disease of MS was come upon around the same time by Friedrich Theodor von Frerichs in Germany and Jean-Martin Charcot and Edmé Felix Alfred Vulpain in France, the former calling it “Hernsklerose”, while Vulpain called it “la sclerose en plaque
dissemineé”(2). Von Frerichs noted the disease’s relapsing-remitting course and that it could evolve to a progressive course over time, as well as the frequency of nystagmus as a symptom. Charcot contributed the eponymous “Charcot’s Triad”, namely nystagmus, intention tremor, and telegraphic speech, as key symptoms diagnostic of MS, though this was later recognised as not entirely specific to MS(2). It was ultimately to Charcot that historical credit would go, though it has been argued that von Frerichs is the more deserved. In parallel with these findings are those by Eduard Rindfleisch, who noted that inflammatory lesions in MS are frequently perivascular, as well as noting its typical onset in patients’ early 20s, and was the first to note the predominance of MS in females relative to males(2).
1.3 The epidemiology of MS
These latter elements discovered by Rindfleisch regarding the distribution of MS in the population, however basic, are fundamental examples of epidemiology, and such information is critical to understanding how any disease works. For any disease, but particularly one so complex as MS, involving such a complex system as the central nervous system, epidemiology is abundantly useful in helping generate hypotheses, and targeting the biomolecular and pathology research which identifies the precise disease processes underway. Similarly basic but fundamental findings as those early studies of MS distribution include showing MS is more common in higher latitude (8, 9), suggesting that latitude and UV may play a role(10), that certain groups are more at risk for MS than others, suggesting a role for genetics(11), that migration affects MS risk(12), suggesting some interplay between genetics and environment on MS risk(13), that herpesvirus exposure may relate to MS risk(14-16), that smoking may relate to exacerbation(17), and that acute infection may relate to exacerbation(18). Such findings are critical to identifying possible factors involved in MS, as well as providing evidence against other not likely to be involved.
1.3.1 MS in Greater Hobart, Tasmania
community and the prevalent population of persons with MS in southern Tasmania has yielded years of fruitful research of global import. The first systematic evaluation of MS epidemiology in Hobart was done by McCall and colleagues(19) in 1961, the initial three-city study of MS in Hobart in Tasmania, Perth in Western Australia, and Newcastle in New South Wales. This study found that despite its small population and geographically peripheral location, Hobart had the highest prevalence and incidence of MS in the nation, double that of Newcastle and Perth. This difference could not be attributed to differences in diagnosis – all cases were diagnosed using the Allison & Millar criteria(20) - and case ascertainment, nor access to care or significant differences in population structure, either age or ethnicity. Thus this study was among the first strong demonstrations of the potent difference in MS frequency by latitude. The follow-up three-city study of Hobart, Perth and Newcastle by Hammond and colleagues(21) in 1981, found Hobart continued to have the highest frequencies in Australia. Moreover, in all three sites, the prevalence of MS had nearly doubled in the 20 years since the preceding study by McCall (Figure 1.5).
Figure 1.5. MS prevalence in Australia: Hobart, Perth and Newcastle, 1961 and 1981.
Figure reproduced from Hammond and colleagues(21)
Here again, the consistent methods used across each of the three sites, including diagnostic criteria – all cases diagnosed by the Rose criteria(22) – and relatively equal access to care and case ascertainment argues against ascription of the difference by site to methodological differences.
After these two studies, however, follow-up studies of MS epidemiology in Australia were relatively few. Hammond and colleagues undertook a study of Queensland(23) and McLeod evaluated the prevalence of MS in the states of New South Wales and South Australia(24), while Simmons evaluated the Australian Capital Territory(25). It was only in 2003, however, that Barnett and colleagues(26) evaluated one of the original three cities, assessing the prevalence in Newcastle in 1997. This study found a continued increase in the prevalence and incidence of MS as in the preceding two studies. No follow-up studies had yet been undertaken to evaluate the frequency of MS in Hobart, however. Thus
was undertaken a study of MS prevalence in 2001 and 2009, and incidence and mortality between 2001 and 2009, the results of which were published in 2011(27) and are reported in Chapter 2.
1.3.2 MS latitudinal gradient
The above-noted excess of MS cases in Hobart relative to the mainland of Australia had long been noted anecdotally by physicians and described generally by early researchers. Sutherland and colleagues(28), using mortality statistics in Australia and New Zealand, estimated the frequencies of MS in the populations above and below latitude 35°S, with those further south having nearly double the frequency of the northern locales. Similar work by Sutherland and colleagues(29) in the Australian state of Queensland found that the frequency of MS in the southern portion of the state (south of the Tropic of Capricorn, 23.5°) was nearly double that of the north; a follow-up study by Hammond and colleagues(23) in 1987 found this persisted. In parallel with work in Australia, studies of MS epidemiology in New Zealand have found a potent association between latitude and MS prevalence, despite the much shorter latitudinal range (33 vs. 12 degrees latitude). Skegg and colleagues(30) found the prevalence in the Southland/Otago region of the South Island to be nearly three-times that of the Waikato region of the North Island. Recently, a comprehensive study of MS prevalence in New Zealand by Taylor and colleagues(31) found this gradient persisted, with the Southland/Otago prevalence over double that of the Waikato region.
While a prototypical region for the study of MS geoepidemiology, given the largely standard medical infrastructure and access to care, and relative culture and ethnic homogeneity, Australasia is not the only region wherein a gradient in MS frequency has been noted. Indeed, anecdotal note of the gradient has been noted in the British Commonwealth nations of the mid-1900s(8), in Europe(32-36), North America(37-40) and Japan(41, 42). Kurtzke was the first to compile all the extant data from MS prevalence studies globally and evaluate their distribution by latitude. From this, Kurtzke(43) described bands of low, medium and high prevalence, increasing with latitude. A subsequent, larger study by
Kurtzke(44, 45) revised this gradient hypothesis slightly, given the much higher prevalence in northern North America relative to Scandinavia, allowing the gradient ranges to vary by longitude(46, 47). Subsequent reviews(48, 49) continued to support the gradient hypothesis, though with increasing note made of exceptions in Scandinavia and Mediterranean Europe. However, in a 1994 review of MS epidemiology in Europe, Rosati(50) argued that the association with latitude was an oversimplification, pointing to studies undertaken in Mediterranean Europe after 1980 which found high prevalence in a Kurtzke medium-prevalence zone(43-45). Rosati next undertook a 2001 descriptive review of MS prevalence globally(51, 52), arguing that the occurrence of aberrations from the gradient demonstrated the oversimplicity of the gradient hypothesis, instead proposing that much of the difference in prevalence distribution was due to variations in genetic susceptibility and study methodologies.
The first meta-analysis of MS geoepidemiology was done by Zivadinov and colleagues in 2003(53), combining data from 69 prevalence and 22 incidence studies between 1980 and 1998. Importantly, in addition to analysing crude values, Zivadinov age-standardised prevalence, finding a significant gradient in the crude analysis (p<0.001), though this was attenuated on age-standardisation (p=0.01). No association between latitude and incidence was found after age-standardisation however (p=0.779). In 2008, Alonso and Hérnan undertook a meta-analysis of MS incidence, reviewing 28 studies with 38 incidence points between 1966 and 2007(54). The authors reported that, in contradistinction to the findings by Zivadinov(53), there was a significant association between incidence and latitude, though weakened after 1980. Recently, Koch-Henriksen and Sørensen(55) published findings from a meta- analysis of 226 MS prevalence and incidence studies, reporting “modest” associations between prevalence and latitude in Europe and North America (p=0.018); with incidence, the authors found no association for Western Europe (p=0.99) or North America (p=0.93). Surprisingly, in Australasia, an archetype of the latitudinal gradient(19, 21, 31), the authors found no association between latitude and
As previous systematic reviews suffered from a number of methodological shortcomings, including