Canadian study finds MS increasing among
women
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Medical Update Memo
October 31, 2006
SUMMARY
Researchers using a Canada-wide database have
found that multiple sclerosis in women has
approximately tripled over the past 60 years
and that the female to male sex ratio now
exceeds three women with MS for every one
man (3.5:1). The study is reported in the
November 2006 issue of Lancet Neurology.
There has been debate about whether MS is
increasing with most observers attributing
an apparent increase to better awareness,
education, more neurologists and MRI scanners
or a combination of all of these. The increasing
sex ratio in Canada precedes changes in diagnostic
probability so these results should resolve
this question. The longitudinal data also
supports the reports from earlier in the
twentieth century that the MS sex ratio was
once one-to-one. The rapid change over a
short period must be environmental but with
a probably interaction with genes. Governments
and health care economists need to take this
new information into account when planning
for current and future expenditures on disease
management and research. The study was funded
by the MS Scientific Research Foundation,
which is related to the Multiple Sclerosis
Society of Canada.
DETAILS
Lead investigators George Ebers, M.D., (University
of Oxford) and A. Dessa Sadovnick, Ph.D,
(University of British Columbia) reported
in the November 2006 issue of Lancet Neurology
that MS has increased in women over the past
60 years. Using a Canada wide-data base of
more than 27,000 people with MS, they found
that the female to male sex ratio now exceeds
3.5 women with MS for every one man (3.5:1)
This ratio was one-to-one in the early decades
of the twentieth century.
The researchers used the database developed
by the Canadian Collaborative Project on Genetic
Susceptibility to MS, which has been funded
by the MS Scientific Research Foundation since
the early 1990s. The Foundation is related
to the Multiple Sclerosis Society of Canada.
The Canadian Collaborative Project has gathered
detailed information about demographics, family
history and clinical aspects of MS from people
with MS attending the participating Canadian
MS clinics.
For this study, the researchers identified
27,074 people with MS born between 1931 and
1980. Of the total, 19,417 were women and 7,657
were men. The participants were grouped into
five-year blocks to calculate the sex ratio
and change in incidence. Comparison of the
sex ratio found a significant, progressive,
gradual increase in the proportion of Canadian
women with MS compared to men and that the
female to male sex ratio of MS has been increasing
in Canada for at least 60 years. There was
no indication that the male rate had changed.
The duration of the change eliminates confounders
such as earlier diagnosis in women, and its
timing long precedes MRI scanning and public
awareness of MS.
Drs. Ebers, Sadovnick and colleagues noted
that the factors causing the increasing number
of women with MS are speculative at this point.
They suggested, given the short time period
in which the increase occurred, the factors
must be environmental in nature, perhaps resulting
from gene-environment interaction. The increase
precedes birth control pills but smoking is
less easily excluded. Other lifestyle factors
mentioned included the higher numbers and changing
roles of women in the workplace, time spent
outdoors, dietary factors and alterations in
the timing of childbearing years. The investigators
suspect a tie-in with the strong maternal effect
found earlier by the study (Ebers et al. Lancet 2004). In this study of half siblings who both
have MS with only one parent in common, the
mother was much more likely to be the common
parent.
Study investigators noted the findings may
provide insights into possible disease causes
and have implications in health care strategies
in managing and treating MS and the focus of
research efforts. The data imply that MS is
preventable in the country of residence, and
that women have an independent or accessory
route to become susceptible to MS. The year
of birth sex ratio appears to provide a simple
way of tracking disease incidence. Year of
birth and sex ratio could be used as measures
for
intervention or prevention studies, according
to Drs. Ebers and Sadovnick.
This study by members
of the Canadian Collaborative Project on
Genetic Susceptibility to MS is one of more
than 50
papers that have been published since the project
began. Collectively, the project has contributed
vital knowledge about genetic aspects of MS
and their relationship to environmental factors,
said Dr. William J. McIlroy, national medical
advisor, Multiple Sclerosis Society of Canada.
ASK MS Information System Code: 2.3.3.c
National Research Department
National Marketing and Communications Department
Disclaimer
The Multiple Sclerosis Society of Canada is an independent,
voluntary health agency and does not approve, endorse or
recommend any specific product or therapy but provides
information to assist individuals in making their own decisions.
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