Article

Multiple sclerosis (MS) is the most frequently seen demyelinating disease, with a
prevalence that varies considerably, from high levels in North America and Europe
(>100/100,000 inhabitants) to low rates in Eastern Asia and sub-Saharan Africa
(2/100,000 population). Knowledge of the geographical distribution of the disease
and its survival data, and a better understanding of the natural history of the
disease, have improved our understanding of the respective roles of endogenous
and exogenous causes of MS. Concerning mortality, in a large French cohort of
27,603 patients, there was no difference between MS patients and controls in the
first 20 years of the disease, although life expectancy was reduced by 6-7 years
in MS patients. In 2004, the prevalence of MS in France was 94.7/100,000
population, according to data from the French National Health Insurance Agency
for Salaried Workers (Caisse nationale d'assurance maladie des travailleurs
Salaries [CNAM-TS]), which insures 87% of the French population. This prevalence
was higher in the North and East of France. In several countries, including
France, the gender ratio for MS incidence (women/men) went from 2/1 to 3/1 from
the 1950s to the 2000s, but only for the relapsing-remitting form. As for risk
factors of MS, the most pertinent environmental factors are infection with
Epstein-Barr virus (EBV), especially if it arises after childhood and is
symptomatic. The role of smoking in MS risk has been confirmed, but is modest. In
contrast, vaccines, stress, traumatic events and allergies have not been
identified as risk factors, while the involvement of vitamin D has yet to be
confirmed. From a genetic point of view, the association between HLA-DRB1*15:01
and a high risk of MS has been known for decades. More recently, immunogenetic
markers have been identified (IL2RA, IL7RA) and, in particular thanks to studies
of genome-wide associations, more than 100 genetic variants have been reported.
Most of these are involved in the immune response and often associated with other
autoimmune diseases. Studies of the natural history of MS suggest it is a
two-phase disease: in the first phase, inflammation is focal with flares; and in
the second phase, disability progresses independently of focal inflammation. This
has clear implications for therapy. Age may also be a key factor in the phenotype
of the disease. In conclusion, France is a high-risk country for MS, but it only
slightly reduces life expectancy. MS is a multifactorial disease and the
implications of immunogenetics are major. Preventative approaches might be
derived from knowledge of the risk factors and natural history of the disease
(smoking, vitamin D).
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