Transcript Slide 1

Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Outcomes from the
MS Forum Modern Management Workshop,
February 2007,
Wiesbaden, Germany
Introduction
• MS is an autoimmune demyelinating disorder of the
central nervous system
• Both environmental and genetic factors contribute
to the aetiology of MS
• No single factor is responsible for conferring
susceptibility – MS is a multifactorial disease
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Epidemiology
• First study of
geographical
distribution of MS
prevalence by
Davenport
• Key finding:
Geographical
variation in MS
prevalence, implying
population (genetic)
and environmental
contributions to MS
risk
This article was published in McAlpine’s Multiple Sclerosis 4th
edition. Compston A. ed. London Churchill Livingstone Elsevier
2006;55 Fig 1.33 Copyright Elsevier (2007)
The Geographical Distribution of MS
Davenport CB. In: Association for Research in Nervous and Medical Conditions (ARNMD), vol 2. New York:
Hoeber, 1921;pp8–19.
• Study in France
confirms that MS
prevalence shows a
gradient roughly
increasing from the
equator even in
homogenous
populations
93
103
82
77
97
100
88
87
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59
84
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Vukusic S et al. J Neurol Neurosurg Psychiat 2007;78:707–709.
J Neurol Neurosurg Psychiat 2007;78:707–9. Reproduced/amended with
permission from the BMJ Publishing Groups
The Geographical Distribution of MS –
Prevalence Increases away from the
Equator
The Effect of Migration on MS Prevalence
140
Prevalence for 100,000
• Non-migrants:
prevalence low
(~20/100 000)
• Migrants: prevalence
increased
(~40/100 000)
• Migrants <15 years
old: prevalence
highest
(~140/100 000)
160
Migrants to a temperate region before the
age of 15 years
Migrants to a temperate region
Migrants to a temperate region after the
age of 15 years
Non-Migrants
120
100
80
60
40
20
0
15–24
25–34
35–44
Age
Cabre P et al. Brain 2005;128:2899–2910.
45–54
55–64
Cabre P, Prevalence of MS in the French West Indies in the West Indian
population aged from 15 to 64 years on 12/31/1999 according to migration
to temperate region, Brain, 2005, 128, 2899–2910, by permission of Oxford
University Press
Immigration studies:
West Indians returning
to French West Indies
from France
French West Indies – MS prevalence (31/12/1999)
Epidemics or Clusters of MS
• 55 cases since 1940
– Four incidence peaks
• Occupied during World
War II
• Authors concluded that
this was evidence of an
MS epidemic caused by
an agent introduced by
the troops
• Evidence of epidemics
has not been replicated
12
10
8
6
4
2
0
1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990
Kurtzke JF et al. Acta Neurol Scand 1993;88:161–173.
Kurtske JF, Multiple sclerosis in the Faroe Islands. 5, Acta Neurol
Scand 1993;88:161–73, Blackwell Publishing Ltd
The annual incidence of MS (per 100 000
inhabitants) in the Faroe Islands since 1940
• No documented cases of
MS on the Faroe Islands
until after World War II
The Geography of MS: Interpretation
Interpretation of geographical and migration data –
three possible factors:
• Infections
– Direct: Many historical candidates but none confirmed
– Indirect: Hygiene Hypothesis, e.g. parasitic
commensalism1
• Chemico-physical environment
– Sunlight
– Vitamin D3
– Diet
• Population genetics
– MS prevalence varies with ethnic ancestry:
Caucasian 1, black 0.5, oriental, 0.1
1
Correale J et al. Ann Neurol 2007;61:97–108.
The Geography of MS: Conclusions
• The aetiology of MS is complex
• There is evidence for both infection and the
chemico-physical environment playing roles
• Additional data are needed to conclusively prove
which factors are important in MS risk
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Genetics
The Genetics of MS: Twin Studies
• High MZ versus DZ concordance rates reflect
genetic factors
• Concordance rates vary with background
prevalence:
– Canada, Denmark,
Finland, UK, USA1
MZ = 25–30% DZ = 3–5%
– France1
MZ = 5.9% DZ = 3%
– Italy2
MZ = 14.5% DZ = 4%
1Willer
CJ et al. PNAS 2003;100:12877–12882; 2Ristori G et al. Ann Neurol 2006;59:27–34.
The Genetics of MS: Twin Studies
• Study of MS concordance among twins by sex,
zygosity and latitude (USA and Canada):1
– MZ concordance rate 1.9 times greater among northern
twins where female concordance is greater
– Variation in MZ concordance rate by latitude is influenced
by environmental and genetic factors
• Under-representation of MS among different twin
populations:
– MZ and DZ twins in Italy
– DZ twins in Sardinia
– DZ twins in Denmark
• Early protective factors shared by twins may reduce
susceptibility to MS
1Islam
T et al. Ann Neurol 2006;60:56–64.
The Genetics of MS: Twin Studies
Longitudinal, population-based study of twins with MS
in Canada
• 75% of Canadian MS twin pairs ascertained
• Twinning had no effect on prevalence
• Twins with MS did not differ for MS risk to their
siblings
• MZ twin concordance >DZ. Excess primarily from
like-sexed female pairs
• No MZ/DZ difference in males
• Non-significant 2-fold increase in risk to DZ twins
over non-twin siblings of twins
Willer CJ et al. PNAS 2003;100:12877–12882.
The Genetics of MS: Half-Sibling Results
• Half-sibling rate of MS in those raised together
versus apart is identical – environment effect
undetectable. Micro-environment effect not seen
• ‘Parent-of-origin’ effect, demonstrated by maternal
versus paternal half-sibling MS rate – mother more
likely to be common parent
• Full sibling rate 3.5% (share 50% of genome),
expect lower (around half) MS rate in half-siblings
(share only 25% of genome)
• Results suggest familial risk not polygenic in nature
and/or polygenes have little influence on the
inheritance pattern
Ebers GC et al. Lancet 2004;363:1773–1774.
The Genetics of MS: The Rate of MS in
Females is Increasing
• No plausible
confounders identified
30
Mean Sex Ratio
• Effect independent of
diagnostic changes
32
28
26
24
22
Mean Sex Ratio
Lower 95% Cl
Upper 95% Cl
20
18
1Orton
SM et al. Lancet Neurol 2006;5:932–936.
Year of Birth
This article was published in Lancet Neurol 2006;5, Orton, Sex
raion of multiple sclerosis in Canada: a longitundinal study, 93236, Copyright Elsevier (2007) Reprinted with permission from
Elsevier (The (Lancet Neurology, 2006, 5, 932–36)
• Female-to-male ratio
increasing with time
Canadian Collaborative Project on Genetic
Susceptibility to Multiple Sclerosis1
R=0.84
The Genetics of MS: Cumulative Effect of
Adding a Shared Environment
Baseline population rate ~1/1000
No additional risk of the shared environment of:
• Conjugal cohabitation1
• Being raised together2 (adoptees,3
half-siblings, step-sibling4)
• Being born close together5
1Ebers
GC et al. Ann Neurol 2000;48:927–931; 2Ebers GC et al. Lancet 2004;363:1773–1774; 3Ebers GC
et al. Nature 1995;377:150–151; 4Dyment DA et al. J Neurol Neurosurg Psychiatry 2006;77:258–259;
5Sadovnick AD et al. Lancet Neurol 2005;4:611–617.
The Genetics of MS: Cumulative Effect
of Adding a Shared Environment –
Conclusion
• No effect of shared familial or cohabitational microenvironment detected except
– DZ twin MS risk greater than full sibling risk but should not
be so, as both share 50% of their genome
• Macroenvironmental factors exert effects at a broad
population level to influence the geographical
distribution of MS
The Genetics of MS: Cumulative Effect of
Adding Shared Genes
• Baseline population rate of 1/1000 – add in the risk
of increasing gene sharing:
–
–
–
–
–
–
–
–
Cousin has MS
Paternal half-sibling
Maternal half-sibling
Full sibling
HLA-identical sibling
Sibling in a consanguineous mating
Offspring of a conjugal pair
MZ twin (~all genes in common)
7/1000
13/1000
24/1000
35/1000
80/1000
90/1000
200/1000
270/1000
• In contrast to the environment, serial increases in
the proportion of genes shared raises the risk of MS
at each level
Ebers GC. Unpublished data.
The Genetics of MS: Which Genes are
Important?
• If many genes exert small effects, MS risk should
decrease in half-siblings versus full siblings – but
does not
– Suggests a few genes exert a large effect – polygenes
have little or no effect on inheritance pattern
• Regions of interest in MS identified on all
chromosomes, but only one confirmed1
• Positive results for HLA Class I/II, T-cell receptor ,
IL7-R2 and cytotoxic T-lymphocyte-associated
protein 43
1Colhoun
HM et al. Lancet 2003;361:865–872; 2Gregory SG, et al. Nat Genet 2007: published online: 29
July 2007. doi:10.1038/ng2103; 3Dyment DA et al. Lancet Neurol 2004;3:104–110.
The Epidemiology and Genetics of MS:
Conclusions 1
• Environmental component of MS susceptibility is
very large:
– Acts early at the population level in susceptible individuals
– Possibly encompasses more than one effect
(e.g. latitude/sun-related +/- via vitamin D3)
• Increased familial risk proportional to degree of
relatedness
• Common microenvironmental exposure does not
explain the familial risk
The Epidemiology and Genetics of MS:
Conclusions 2
• The findings don’t support predictions from
polygenic models
• HLA Class II probably contains the major/only locus
for susceptibility. Higher order interactions are key
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Sunshine and Vitamin D3
Potential Effects of Sunshine Exposure
Potential effects of sunshine exposure on the human
body include:
• Circadian rhythm1
• Nervous system2
• Immune system2,3
• Vitamin D3 synthesis2
1Hastings
M. BMJ 1998;317:1704–1707; 2Wurtman R. Sci Amer 1975;223:69–77; 3Schwarz T.
Keio J Med 2005;54:165–171.
Biological Effects of Sunshine: Circadian
Rhythm
• Several systems that convey light information to the
body could be responsible for modulating MS
– E.g. the human circadian rhythm regulated by light
• Circadian rhythms facilitate physiological fine-tuning
to variable activity and rest
• Human 24-h clock co-ordinated by a master time
switch in suprachiasmatic nuclei, by eyes detecting
the light–dark cycles
• Immune reactivity differs during the cycle
Circadian Rhythm: Evidence for Novel
Ocular Photoreceptor
• Circadian system cannot be set by light in the
absence of eyes
• Circadian and visual systems process light
differently:
– Circadian system processes the entire visual field
(irradiance)
– Visual system captures light from a specific region
• Visually blind mice (no rods/cones) use light to
regulate circadian rhythms and melatonin
production1,2
• These findings indicated that a third ocular
photoreceptor cell existed – the retinal ganglion
cells3
1Freedman
507;
MS et al. Science 1999;284:502–504; 2Lucas RJ et al. Science 1999;284:505–
S et al. Current Biology 2003;13:1290–1298.
3Sekaran
• Retinal ganglion cells
photoreception play
dominant roles in:
5
– Pupil constriction1
– Temperature
– Alertness and mood2
– Sleep induction
• Seasonal affective disorder
shows the same latitude
association as MS
10
More alert
– Heart rate
Alertness
15
20
25
10
1Lucas
RJ et al. Nat Neurosci 2001;4:621–626; 2Cajochen C et al.
Behav Brain Res 2000;115:75–83.
100
1000
10,000
Illuminance (lux)
This article was published in Behav Brain Res, 115, Cajochen C, Dose-response
relationship for light intensity and ocular and electroencephalographic
correlates of human alertness, 75–83, Copyright Elsevier (2007)
Role of Retinal Ganglion Cells
Biological Effects of Ultraviolet Radiation
on Vitamin D3
7-dehydrocholesterol
• Vitamin D3
• Generated in animal skin when light energy
is absorbed by a precursor molecule
(7-dehydrocholesterol)
In skin
HO
cholecalciferol (vitamin D3)
• Inactive until converted to the hormonallyactive form (1,25(OH)2D3)
• Many effects on the immune system
including:
In liver
HO
25-hydroxycholecalciferol
(25-hydroxy vitamin D3)
– Receptors for 1,25(OH)2 vitamin D3 found on
immune cells
– Inhibits interleukin-2 production
– Reduces symptoms in murine EAE
– Broad spectrum whole body irradiation
reduces murine EAE development
OH
In kidney
HO
1,25-dihydroxycholecalciferol
(1,25-dihydroxy vitamin D3)
OH
ACTIVE
FORM
HO
OH
• Depletes Langerhans cells
[1]
• Stimulates keratinocytes
to release
immunosuppressive
mediators (IL-10 and TNF) leading to systemic
immunosuppression [2]
• Converts trans-urocanic
acid (UCA) to cis-UCA
(immunosuppressive) [3]
• Suppresses expression of
MHC Class II and costimulatory molecules [4]
(e.g. B7)
Schwarz T. Keio J Med 2005;54:165–171.
Depletion of
Langerhans cells (LCs)
1
UVB
2
3
trans-UCA
4
dendritic
cell
cis-UCA
keratinocyte
B7
MHC
Ag
CD
28
IL-10
TNF-
T-cell
'tolerance'
TCR
CD
4
T-lymphocyte
Reproduced with permission from Schwarz T. Keio J Med 2005;54:165–171
Biological Effects of Ultraviolet Radiation
on the Immune System
Biological Effects of Vitamin D3 on the
Immune System – Immune Modulation
Vitamin D3 is a potent immune modulator:
• Enhances dendritic cell apoptosis and macrophage
phagocytosis
• Enhances activity of natural killer cells
• Induces expression of the tolerigenic cytokine IL-10
and the Toll-like receptor co-receptor CD14
• Induces expression of antimicrobial peptides
Biological Effects of Vitamin D3 on the
Immune System – Immune Modulation
• Inhibits DC maturation
• Inhibits the function of IL-1 (pro-inflammatory)
• Inhibits production of Th1-inducing cytokines
• Inhibits transcription of IFNγ target genes and the
gene encoding neutrophil chemotactic factor IL-8
• Exhibits anti-tumour activity
Activation of Tolllike receptors (TLRs)
stimulates innate
immune response
• Up-regulates
expression of
vitamin D3 receptor,
vitamin D-1hydroxylase genes
and production of
antimicrobial
peptides, e.g.
cathelicidin
Liu PT et al. Science 2006;311:1770–1773.
Reproduced with permission from Bruce Hollis
Vitamin D3 Induces Antimicrobial
Peptides
Vitamin D3 and the CNS: Biological
Effects
Diverse effects on the vertebrate nervous system –
protects against premature cell loss
• Induces nerve growth factor expression
• Protects against oxidative damage
• In rats:
– Retards age-related decreases in hippocampal neuronal
density
– Inhibits expression of markers (L-type voltage-gated
calcium channels)
– Protects against neuronal cell death in stroke model
The Main Biological Effects of Vitamin D3:
Summary
• Calcium homeostasis
– Regulates calcium and phosphorous levels by promoting their
absorption from food
– Promotes re-absorption of calcium in the kidneys
– Promotes bone formation and mineralisation
• Cancer chemoprevention
– Vitamin D3 supplementation correlated with reduced risk of some
cancers
• Neuroprotection
– Induces expression of nerve growth factor
– Protects against reactive oxygen species-induced oxidative
damage
• Immune system regulation
– Promotes immunosuppression, phagocytosis by macrophages,
anti-tumour activity
Role of Vitamin D3 in Evolution:
Early History
• Earliest phytoplankton/diatoms produced ergosterol
– Converted to previtamin D2
– Acted as a sunscreen
– Allowed calcium sequestration
• Ingestion of previtamin-D2-rich phytoplankton
– Facilitated incorporation of environment calcium into
exoskeletons, then endoskeletons in fish
• Previtamin D3 synthesis in vertebrate skin – a key
innovation facilitating dry land colonisation
Role of Vitamin D3 in Evolution: Skin
Pigmentation
• Humans originated in Africa,
where UVB levels were high
• Dark skin was the original
ancestral condition for the
genus Homo
Courtesy of Mauricio Antón
• Skin with more melanin
protects from UV radiation
harm
• Most organisms exposed to
sunlight have melanin in their
tegument
Reconstruction of Homo ergaster
by Mauricio Antón
Role of Vitamin D3 in Evolution: Melanin
• Absorbs/scatters UV
radiation
• Neutralises reactive
oxygen species
(damage DNA)
Skin
• Occurs widely in nature
and slows vitamin D3
production in skin
– Problematic for the darkskinned living outside
tropical latitudes as UVB
levels fall with increasing
latitude
Melanosome
COOH
HO
O2
NH2
Tyrosine
HO
HO
COOH
NH2
DOPA
Tyrosinase
O2
EUMELANIN
O
PHEOMELANIN
O
COOH
NH2
DOPAquinone
Courtesy of Jennifer Kane
Melanocyte
Sunshine Implicated in Several Diseases
Reduced sunlight exposure has been linked
to rickets and possibly to:
• Autoimmune diseases:
– MS
– Rheumatoid arthritis
– Type 1 diabetes
• Cancer (other than skin cancers)
• Seasonal Affective Disorder
Holick MF. Am J Clin Nutr 2004;80:1678S–1688S.
• Result of vitamin D3 deficiency
• Was common in northern countries
in light-skinned people
• Increasing in equatorial countries in
dark-skinned people due to reduced
UVB exposure:
– Spending more time indoors
– Wearing more protective clothing
• Reduces pelvic diameter making
natural childbirth impossible
• Drove natural selection of lighter
skin with migration from the equator
Photo courtesy of and with permission from Tom D Thacher, MD
Role of Vitamin D3 in Evolution:
Vitamin D3 Deficiency – Rickets
Age-standardised MS prevalence
(per 100,000)
•
•
•
•
MS prevalence greater with increasing latitude in Australia1,2
MS prevalence decreased with increasing light exposure
Ultraviolet B light/sunlight correlates with latitude
In Tasmania, higher sun exposure (6–15 years) associated
with decreased MS risk. Higher exposure probably more
important in winter than summer
Latitude
80
80
Sunlight
80
70
70
70
60
60
60
50
50
50
40
40
40
30
30
30
20
20
20
10
10
10
0
0
0
0 15
20
25
30
35
40
Latitude (degrees)
1van
45
UVB
0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
Average annual
bright sunshine (h)
0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Reproduced with permission from van der Mei IA et al.
Neuroepidemiology 2001;20:168–174. van der Mei IA et al. BMJ
2003;327:316–321 and S Karger AG, Basel
Biological Effects of Sunshine on the
Nervous System: Light Exposure and MS
Average annual
ultraviolet radiation (kJ/m2/day)
der Mei IA et al. Neuroepidemiology 2001;20:168–174; 2van der Mei IA et al. BMJ 2003;327:316–321.
Role of Vitamin D3: UVB and
MS Prevalence
• Skin colour darkens in
relation to increasing UVR
exposure in autumn1
93
• Minimum autumn UVR
exposure may be
important, rather than
maximum summer
exposure2
• Higher MS prevalence
correlates with lower UV
levels in France (map) and
the USA
• Unclear if skin colour per se
affects MS risk
1Jablonski
103
82
77
100
88
98
87
62
59
Department
UVMed MIN
3–4
4–6
6–7
7–9
84
47
76
70
78
95
71
55
51
53
51
Courtesy of George Chaplin and George Ebers
(unpublished data)
MS Prevalence by Department
Against UVMED Minimum
10–11
11–13
14–16
NG, Chaplin G. J Hum Evol 2000;39:57–106; 2Chaplin G. Am J Phys Anthropol 2004;
125:292–302.
45
Observed/expected
no. of births
Possible role of light exposure in MS supported by impact
• Of birth month on MS prevalence1
• In the northern hemisphere, significantly more (9.1%) people
with MS born in May (less light during pregnancy) than
November (8.5% – more light during pregnancy). Birth month
effect is inverse in the southern hemisphere
1.15
1.10
Pooled analysis of observed/expected
births in people with multiple sclerosis
in Canadian, British, Danish and
Swedish studies (n=42 045) with 95%
confidence intervals
1.05
1.00
0.95
0.90
0.85
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1Willer
Month
CJ et al. BMJ 2005;330:120–125.
BMJ 2005;330:120–125 reproduced/amended
with permission from the BMJ Publishing Groups
Biological Effects of Sunshine on the
Nervous System: Birth Month and MS
Ultraviolet Radiation and MS: Summary
• MS prevalence in Australia closely predicted by
regional UVR levels1
• Higher sun exposure (6–15 years) associated with
decreased risk of MS2
• Similar findings in France linking increased
prevalence of MS with low UVB exposure
• In northern Europe and Canada, May birth increases
MS risk, suggesting low UV radiation levels during
pregnancy may be involved3
1van
der Mei IA et al. Neuroepidemiology 2001;20:168–174; 2 van der Mei IA et al. BMJ 2003;327:316–
321; 3Willer CJ et al. BMJ 2005;330:120–125.
Vitamin D3: The Link between Sunshine
and MS
• Sunshine may affect MS risk via vitamin D3
• Higher circulating levels of 25-hydroxyvitamin D3
associated with a lower risk of MS in whites
– Not black and Hispanic individuals1
• 1,25-dihydroxyvitamin D3 inhibited EAE induction in
mice, preventing disease progression2
1Munger
KL et al. JAMA 2006;296:2832–2838; 2Cantorna MT et al. PNAS 1996;93:7861–7864.
Properties of Vitamin D – Two Types
• Vitamin D2
– Formed by irradiation of ergocalciferol, found in plants
– Provided by some dietary sources and multivitamins
– Biologically inert
– Conversion (hydroxylation) in the liver and kidneys produces the
active form 1,25-dihydroxycholecalciferol (1,25(OH)2D3)
– D2 is less potent than D3
• Vitamin D3
– Naturally occurring form in humans
– Formed in skin by UV light action on vitamin D precursors
– Present in certain nutrients
– Biologically inert
– Conversion (hydroxylation) in the liver and kidneys produces the
active form 1,25(OH)2D3
Sources of Vitamin D3 in Humans
• Sources of vitamin D3:
– Natural dietary sources limited, e.g. fish oils, fatty/oily fish,
cod-liver oil
– Cutaneous generation of vitamin D3
• Cutaneous vitamin D3 production is very efficient
– Depends on amount of UVB radiation falling on the skin
and the skin tone
• A single initial MED of UVB radiation to a lightskinned individual releases approximately 20 000 IU
vitamin D3 into the circulation within 24 h
– Dark-skinned individuals probably require a 10-fold greater
exposure time
Vitamin D3 in Humans: Sunshine and
Skin Colouration
Months/year when sunshine cannot produce sufficient vitamin D3 in the skin1–3
No vit D for >6 m/y
No vit D for 1–6 m/y
No vit D for 1–6 m/y
No vit D for >6 m/y
Theoretical skin colour based on environmental variables1–3
1Jablonski
NG, Chaplin G. J Hum Evol 2000;39:57–106; 2Jablonski NG, Chaplin G. Scientific American
2002;287:74–81; 3Chaplin G. Am J Phys Anthropol 2004;125:292–302.
Courtesy of Sarah Chen
Vit D all year
Vitamin D3 in Humans: Supplementation
• Many populations need higher sunlight exposure to
increase endogenous vitamin D3 production
– Would increase skin cancer risk in light-skinned individuals
• Dark-skinned individuals living in northern
Europe/USA cannot spend enough time in the sun
to make sufficient vitamin D3
• Oral vitamin D3 supplementation should be given
strong consideration
Vitamin D3 in Humans: Optimum
Circulating Levels
Circulating 25(OH)D3 levels as related to oral vitamin D3 intake
10,000 IU/d
25(OH)D (mmol/L)
200
5,000 IU/d
150
100
1,000 IU/d
0 IU/d
50
0
0
20
40
60
80
Time (days)
Heaney RP et al. Am J Clin Nutr 2003;77:204–210.
100
120
140
160
Permission granted by American Society of Nutrition
Am J Clin Nutr 2003;77:204–10.
250
Vitamin D3 in Humans: Are we
Getting Enough?
• During winter months in high latitudes, insufficient vitamin D3
synthesised
• US Nutrition Guidelines: LOAEL for vitamin D3 in humans is
2000 IU/day
– Probably too low
• A 1971 study gave ‘normal’ values for 25(OH)D3 from healthy
volunteers when data from lifeguards (higher UVB radiation
exposure) were more relevant1
• Humans probably need higher daily vitamin D3 supplements
than currently permitted
• Recommended daily vitamin D3 intake probably too low2
• The tolerable upper intake level for vitamin D3 should probably
be raised from 2000 IU/d to 10 000 IU/d3
1Haddad
JG, Chyu KJ. J Clin Endocrinol Metab 1971;33:992–995; 2Vieth R et al. Am J Clin Nutr
2007;85:649–650; 3Hathcock JN et al. Am J Clin Nutr 2007;85:6–18.
Can Serum Levels of 25(OH)D3 Predict
MS Risk?
• Objective:
– To evaluate whether prior serum levels predict MS risk in
healthy adults
• Methods:
– Prospective study on >7 million US military personnel
• Results:
– 257 adults with MS and 514 controls
– In whites, risk of MS significantly decreased with increasing prior
levels of 25(OH)D3
– Elevated 25(OH)D3 levels in whites more protective at
younger ages
• Conclusions:
– High circulating levels of vitamin D associated with lower risk
of MS
Munger KL et al. JAMA 2006;296:2832–2838.
Effect of Vitamin D3 on Viral Infection
• 20 μg/d (800 IU/d) reduced incidence of colds and flu in
African American women during the winter
Number of patients
25
Placebo
Vit D 20 mcg/d
20
Vit D 50 mcg/d
15
10
5
0
Winter
Spring
Summer
Season
Aloia JF et al. Epidemiol Infect 2007;12:1–4. Epub ahead of print.
Fall
Permission granted by Aloia JF et al. Epidemic influenza
and vitamin D, 2007 Epub ahead of print. Epidemiol Infect
and Cambridge University Press
• Vitamin D3 supplementation associated with reduced risk of
colds and flu
MS in Norway
• Lower incidences of MS in coastal fishing areas than
inland farming/dairy areas1
– Lower butter/animal fat intake in coastal dwellers1
• Inverse relationship with vegetable and/or fish
intake in the same region was smaller in magnitude,
suggesting confounding factors2
1Swank
RL et al. N Engl J Med 1952;246:722–728; 2Lauer K. Neurology 1997;49:S55–S61.
Prevalence of MS in Norway
• Prevalence data for counties in Norway (/105):
– A Finnmark1 (2003)
>83
– B Troms1 (2003)
>104
– C Nordland (1999)
106
– D Nord Trøndelag (1999)164
C
– E Oppland2 (2002)
190
– F Hordaland (2003)
151
D
– G Oslo2 (2005)
154
• In Norway, MS prevalence does not rise
with increasing latitude, unlike other
northern European countries and the USA
E
• As expected, measured UV radiation
G
levels decrease with increasing latitude
F
1Kampman
MT et al. J Neurol 2007;254:471–477. 2Personal communication.
A
B
A Study of Childhood Environmental
Factors in Norway
• Aim: To assess whether vitamin D3-related
environmental factors in childhood and adolescence
are associated with MS risk at latitudes of 66–71°N
in Finnmark and Troms
– Ultraviolet radiation exposure
– Dietary vitamin D3 intake
– Use of cod-liver oil supplements
• Design: Questionnaire data from 152 MS patients
and 402 controls analysed using conditional logistic
regression analysis accounting for the matching
variables age, sex and birthplace
Kampman MT et al. J Neurol 2007;254:471–477.
A Study of Childhood Environmental
Factors in Norway
Unadjusted odds
ratio
Summer
outdoor
activities
OR†
95% CI
Age 16–20
0.54
0.38–0.75
Age 11–15
0.70
Age 6–10
0.69
Pvalue
Adjusted odds
ratio*
Pvalue
OR†
95% CI
0.001
0.55
0.39–0.78
0.001
0.52–0.96
0.025
0.74
0.54–1.01
0.055
0.51–0.93
0.013
0.71
0.52–0.96
0.025
The regression analysis included 111 patients and 246 controls with complete data for all variables.
*Adjusted for use of cod-liver oil supplementation and meals of boiled or fried fish.
†Odds ratio per one unit change in summer outdoor activities.
Kampman MT et al. J Neurol 2007;254:471–477.
Reproduced from Kampman MT et al. Outdoor activities and diet in
childhood and adolescence relate to MS risk above the Arctic
Circle. Table 2. J Neurol 2007;254:471–477. Copyright granted by
Springer
Odds ratio for MS and summer outdoor activities
A Study of Childhood Environmental
Factors in Norway
Number of
patients/
controls*
OR
95% CI
P-value
132/295
0.73
0.44–1.21
0. 222
Low outdoor activities§
81/118
0.57
0.31–1.05
0.072
High outdoor activities§
63/196
1.18
0.57–2.46
0.657
Matched analysis†
Subgroup analysis‡
*Lower
numbers in matched analysis due to missing data; †Conditional logistic regression;
‡Unconditional logistic regression, adjustment for age and sex, stratification for summer outdoor
activities age 16–20; §Low outdoor activities = not that often/a moderate amount; high outdoor
activities = quite a lot/virtually all the time.
Kampman MT et al. J Neurol 2007;254:471–477.
Reproduced from Kampman MT et al. Outdoor activities and diet in
childhood and adolescence relate to MS risk above the Arctic
Circle. Table 4. J Neurol 2007;254:471–477. Copyright granted by
Springer
Odds ratio for MS and use of cod-liver oil supplements
A Study of Childhood Environmental
Factors in Norway – Conclusions
• Results support the UV radiation/vitamin D3
hypothesis for MS:
– Summer outdoor activities in childhood and adolescence
associated with reduced risk of MS even north of the Arctic
Circle
– Significant effect of outdoor activities related to time spent
outdoors in the summer when vitamin D3 synthesis occurs
– Supplemental cod-liver oil may be protective when sun
exposure reduced
Kampman MT et al. J Neurol 2007;254:471–477.
Vitamin D3 in Humans: Conclusions
• Circulating levels of 25(OH)D3 <32 ng/ml should be considered
deficient by physicians
• A 200 IU/d adequate intake for vitamin D3 is possibly too low
for adults
• The lowest observed adverse effect level in adults (2000
IU/day) should be revised
– Intake for adults probably 2000 IU/d with higher levels for special
cases, e.g. pregnancy
• Chronic nutritional vitamin D3 deficiency may increase the risk
for developing chronic diseases, e.g. cancer, autoimmune
diseases
• High circulating levels of vitamin D3 may decrease MS risk
• Norway is a key exception to the latitude gradient
– May indicate a dietary–latitude interaction
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Infections
Parasites and MS – The Hygiene
Hypothesis
• Many factors apart from sunlight exposure change
with latitude
– E.g. parasite load decreases with increasing latitude
• Hygiene hypothesis – MS prevalence correlates with
a high level of childhood sanitation
• Parasite infections in MS patients might alter the
disease course, e.g. reducing the relapse rate1
• Could early exposure to parasites reduce the risk of
autoimmunity?
1Correale
J et al. Ann Neurol 2007;61:97–108.
Infectious Aetiology of MS: Possible
Candidate Microorganisms
• Chlamydia
• Rubella
• Herpesviruses
• HTLV-1
– HHV-6
• HERV
– HSV
• Corona virus
– CMV
– EBV; HHV-4
– VZV
• Canine distemper virus
• Measles virus
Soldan SS et al. Nat Med 1997;3:1394–1397.
• Bordetella pertussis
• Mumps virus
Infectious Aetiology of MS:
HHV-6, Chlamydia
• Evidence to support HHV-6:
– Increased titres of HHV-6 in MS – association
controversial1–4
– HHV-6 showed a positive association in 29/37 MS studies5
– Positive association in 78% of studies (n=38) if active and
latent virus differentiated6; in 55% (n=20) if pooled6
• Evidence to support chlamydia:
– Conflicting reports with both positive7 and negative data8
– Meta-analysis (26 studies – 1332 MS patients, 1464
controls). Findings insufficient to establish aetiological
relationship9
1Sanders
VJ et al. J Neurvirol 1996;2:249–258; 2Soldan SS et al. Nat Med 1997;3:1394–1397;
3Ablashi DV et al. Mult Scler 1998;4:490–496;4Ablashi DV et al. J Clin Virol 2000;16:179–191;
5Ablashi DV. http://www.hhv-6foundation.org/febpressrelease.pdf; 6HHV Foundation. www.hhv6foundation.org;7 Munger KL et al. Epidemiology 2003;14:141–147; 8Munger KL et al. Neurology
2004;62:1799–1803; 9Bagos PG et al. Mult Scler 2006;12:379–411.
EBV and MS Risk –
Epidemiological Evidence
• Risk of MS following infectious mononucleosis
(symptomatic EBV infection) persists for 3 decades1
• MS risk very low in people never infected with EBV2
– >99% of MS patients infected with EBV (~90% of
controls)3
• EBV has a potential role in MS aetiology in many
sero-epidemiology studies4–8
• MS cluster occurred in 8 children after a glandular
fever outbreak – all had an identical EBV subtype9
1Nielsen
TR et al. Arch Neurol 2007;64:72–75; 2Thacker EL et al. Ann Neurol 2006;59:499–503;
3Ascherio A et al. Epidemiol 2000;11:220–224; 4Ascherio A et al. JAMA 2001;286:3083–3088;
5Levin LI et al. JAMA 2003;289:1533–1536; 6Levin LI et al. JAMA 2005;293:2496–2500;
7Sundstrom P et al. Neurology 2004;62:2277–2282; 8DeLorenze BN et al. Arch Neurol 2006;63:839–844;
9Munch K et al. Acta Neurol Scand 1998;98:395–399.
Infectious Aetiology of MS: EBV and
Paediatric MS Risk
• In paediatric MS studies:
– Serological evidence of EBV greatest in patients with MS
Country
MS patients
Non-MS patients
Canada1
83%
42%
(n=30)
(n=143)
P<0.001
Multinational study2
~80%
40%
(n=72)
(n=69)
P<0.05
Germany3
98.6%
72.1%
(n=147)
(n=147)
P=0.001
1Alotaibi
3Pohl
S et al. JAMA 2004;291:1875–1879; 2Banwell B et al. ECTRIMS 2004, Vienna, P280;
D et al. Neurology 2006;67:2063–2065.
Role of EBV in MS Aetiology –
Biological Evidence
• Antibodies in the spinal fluid of MS subjects
recognise EBV antigens1,2
• Autoimmune T-cells of an MS patient also
recognised EBV3
• MS patients have a higher number of CD8+ T-cells
that recognise EBV than control subjects4
• EBV reactivation may be associated with increased
gadolinium-enhanced MRI activity5
1Bray
PF et al. Neurology 1992;42:1798–1804; 2Cepok S et al. J Clin Invest 2005;115:1352–1360;
3Lang HLE et al. Nat Immunol 2002;3:940–943; 4Höllsberg P et al. Clin Exp Immunol 2003;132:137–143;
5Buljevac D et al. J Neurol Neurosurg Psychiatry 2005;76:1377–1381.
Potential Mechanisms of EBV
Involvement in MS
• Autoimmune
– Molecular mimicry1,2
– Immortal B-cell and plasma cell theory3
– Hygiene hypothesis
• Oligodendrocyte infection
– New symptomatic MS lesions contain evidence of extensive
oligodendrocyte apoptosis and microglial activation in
tissue containing few or no lymphocytes or myelin
phagocytes4
• Dual virus infection
– MS-associated human endogenous retrovirus (HERV)5
• As-yet unknown mechanisms
1Lang
HLE et al. Nat Immunol 2002;3:940–943; 2van Sechel AC et al. J Immunol 1999;162:129–135;
3Pender MP. Trends Immunol 2003;24:548–588; 4Barnett MH, Prineas JW. Ann Neurol 2004;55:458–468;
5Christensen T. Rev Med Virol 2005;15:179–211.
Infectious Aetiology of MS: Summary
• EBV infection in >99% of MS patients (~90% of
controls)1
• MS rare in those without prior EBV infection
• Lymphocytes in patients with active MS have an
increased tendency to undergo spontaneous in vitro
transformation
• Higher risk of developing MS following symptomatic
EBV infection/glandular fever than if no prior history
• People with higher EBV antibody levels have a
greater MS risk compared with those with low
antibody levels2,3
1Ascherio
3Pohl
A et al. Epidemiol 2000;11:220–224; 2Banwell B et al. ECTRIMS 2004, Vienna, P280;
D et al. Neurology 2006;67:2063–2065.
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
Immunity and the Environment
Immunity and the Environment:
Environmental Influence in Mice and Rats
Experimental models of MS (EAE) and arthritis (CIA)
identify environmental factors influencing
susceptibility:
• Protective factors
• Risk factors
– Pregnancy
– Ageing
– Oestrogen
– Post-partum period
– Stress (predator)
– Stress (grouping)
– Light
– Darkness
– Winter–spring
– Summer–autumn
– Parasites (adjuvant)
– Parasites (adjuvant)
Immunity and the Environment:
Conclusions from Animal Studies
• Can neutralise environmental and genetic
interactions in animal models – allows identification
of disease-associated genes/pathways
• Strong environmental effects seen in MS and
arthritis animal models
• Animal studies may identify novel pathways
involved in the aetiology of MS and provide targets
for MS therapy
The Immune System and the
Environment
• The immune system
– Protects host from ‘foreign’ agents, usually from the
environment
– Recognises ‘self’ and ‘non-self’ antigens
• Recognition of ‘non-self’ antigen generally results in
an immune response. Immune system is usually
tolerant of ‘self’ antigens
• Basic components of the adaptive immune system:
– T-cells expressing T-cell receptors (TCRs)
– Antigen-presenting cells (APCs)
• HLA molecules play a key role in immunity and thus
in interactions with the environment
HLA and the Environment: Antigen
Presentation to T-Cells
HLA molecules are crucial for initiating an immune
response against foreign antigens
Antibody
B-cell
’Help’
CD4
T-cell
Antigen
1
3
2
TCR
HLA
APC
HLA and the Environment: Genetic
Control of Survival in Epidemics
1845, 367 Dutch people emigrated to Surinam
• 2 weeks after arrival,
180 died of typhoid fever
• 2 years later, 37 died of
yellow fewer
• In 1978, 4th-generation
survivors tested for 26
polymorphic genes (e.g.
blood types and HLA)
De Vries RR et al. J Immunogenet 1979;6:271–287.
HLA and the Environment: Genetic
Control of Survival in Epidemics
Frequency of blood type and HLA alleles
Surinam survivors n=64
Allele frequency
0.2
Dutch blood donors n>800
0.15
0.1
0.05
0
Rhesus cDE
HLA-B7
De Vries RR et al. J Immunogenet 1979;6:271–287.
HLA-Bw38
HLA and the Environment: Epidemic
Survival and Disease Association
• Expression of rare HLA alleles may be associated
with survival in epidemics:
– Probably due to interactions between humans and viruses,
resulting in viruses targeting more common HLA alleles
during their adaptation to the host
• HLA allele expression is not evenly distributed:
– Particular alleles are seen in specific populations
– Particular alleles are associated with increased risk of
various autoimmune diseases
HLA and the Environment:
HLA-associated Diseases
Considerable data on HLA haplotype frequencies and
autoimmune diseases
Phenotype frequency
DR4
DR3
100
DR4
DR2
B27
B47
Patients
Healthy controls
50
0
MS
CD
RA
IDDM
CAH
Autoimmune diseases
AS
HLA and the Environment: HLA and MS
MS association with the DRB5*0101, DRB1*1501,
DQA1*0102, DQB1*0602 haplotype
DQB1 DQA1
*0602
*0102
DRB1 DRB5
DRA1
*1501 *0101 *0101
DR2 haplotype
(‘European’)
DR2 haplotype
(‘European’)
*zzzz *xxxx
*xxxx *yyyy
DQ6 haplotype
(‘African’)
HLA and the Environment: HLA and MS
• More extensive linkage disequilibrium in HLA-DR2
haplotype than other Caucasian HLA haplotypes in
the DR region
– Maintained by positive selection?1,2
– Alleles inherited together as they co-operate to shape the
T-cell repertoire
• Linkage disequilibrium between DR2b and DR2a
(MS-associated HLA-DR alleles at separate loci):1
– A functional epistatic interaction likely
– Epistasis between DR2b and DR2a alleles associated with
milder EAE
– (see next slide for diagram)
1Gregersen
JW et al. Nature 2006;443:574–577; 2Trowsdale J. Nat Med 2006;12:1119–1120.
HLA and the Environment: HLA and MS
a
?
b
DR2b
DR2a
APC
DR2b
APC
MHCII
MBP peptide
EBV peptide
T-cell
proliferation
Activationinduced
cell death
Severity
of MS
MBP peptide
T-cell
proliferation
Severity
of MS
Time
Primary, progressive MS
Trowsdale J. Nat Med 2006;
12:1119–1120.
Time
Relapsing, remitting MS
Reprinted by permission from Macmillan Publishers Ltd: (Nat
Med 2006;12:1119–1120) copyright (2007)
http://www.nature.com/naturemedicine
MHC haplotypes
HLA and the Environment: Molecular
Mimicry in MS
T-cell cross-reactivity might lead to autoimmunity
Common viral
infection in the
periphery
CD4
T-cell
TCR HLA
Cross-reaction
to myelin antigen
APC
CD4
T-cell
TCR HLA microglia
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors:
Summary (1)
• Twin concordance varies with background prevalence
– Affected by environmental factors
• Familial risk increases with proximity to index case
– Identical twins have the highest risk of MS
• Dizygotic twins have a higher risk than siblings, suggesting
gestational environmental factor(s)
– Supported by the maternal ‘parent-of-origin’ effect in half-siblings
• Month-of-birth data implicate a season-related environmental
factor influencing the developing foetus
• Risk of MS increases with increasing latitude – probably linked
to sunlight exposure
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors:
Summary (2)
• Sunlight may operate via cutaneous vitamin D3 synthesis
– Affected by sunlight exposure and skin tone
• As ancient dark-skinned humans migrated from the equator to
less solar radiation, selective pressure drove the development
of lighter skin tones
– Possibly mediated by vitamin D3 synthesis and the risk of rickets
or parasitic infections
• Skin tone related to autumnal UVB exposure
• Effects of differential exposure to sunlight on MS risk can be
offset by a high dietary vitamin D3 intake
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors:
Summary (3)
• Vitamin D3 is important for maintaining health
• Current recommended daily vitamin D3 intake combined with
low levels of cutaneous synthesis may be too low
• Vitamin D3 is a strong candidate for determining MS
susceptibility, but other sunlight-related factors may be
involved
• Sero-epidemiological evidence suggests that EBV exposure
increases MS risk
– More evidence needed to confirm a causal link rather than an
association
– EBV infection does not guarantee MS
• Effect of MHC is complex – linkage disequilibrium between
Class I and II important in MS
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors:
Conclusions
• Environmental effects in MS are very important and
act at a population level
• Sunlight, probably mediated via vitamin D3, is a
strong environmental candidate
• Vitamin D3 could be a common mediator of the
latitude effect
• Circumstantial evidence points to EBV but other
autoimmune diseases show high anti-EBV titres
Multiple Sclerosis: Epidemiology,
Genetics and Environmental Factors
How could the various factors interact to cause MS?
Genetically susceptible individuals
(HLA haplotype)
Lack of sunlight or vitamin D3 during gestation
and/or early life (latitude- or skin tone-related)
Developmental alterations may result from deficiency in
sunlight interfering with the maturation of the nervous
and/or immune systems and the establishment of tolerance
Tolerance breakdown precipitated by viral infections and
non-specific immune stimulation (EBV?)