Investigators Explore MS Risk Conferred
by Combination of Gene and Virus
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Medical Update Memo
April 22, 2008
SUMMARY
A new study suggests that if a person has
a specific gene and has high serum levels of
antibodies to a specific virus, the person’s
risk of developing multiple sclerosis is greatly
magnified, much more than having either risk
factor alone.
DETAILS
Drs. Philip De Jager, Alberto Ascherio and
colleagues from Harvard and other institutions
found that those with two previously identified
MS risk factors – an immune gene known
as HLA DR15 and antibodies to the Epstein-Barr
virus in the blood serum – were nine
times more likely to develop MS than those
without that gene and with low levels of
viral antibodies. The study, published in
a special MS-themed issue of the journal
Neurology (70: 1113-18 March 25, 2008 Part
2), underscores the importance of studying
as yet little understood interactions between
genes and the environment that contribute
to MS susceptibility.
Background:
MS is thought to occur when people
whose genes make them susceptible encounter
something in their environment that triggers
this immune-based neurological disease. Although
several genes probably contribute to susceptibility,
specific genes that have been shown to confer
higher susceptibility to MS are called HLA
DR15, which help control how the immune system
identifies targets. Many infectious agents
have been investigated at various times as
possible triggers of MS, but no single virus
or bacterium has been proved to cause the disease.
However, previous studies have suggested that
a past history of infectious mononucleosis
(caused by the Epstein-Barr virus, or “EBV”)
or high levels of blood serum antibodies that
fight EBV increase the risk for developing
MS.
This Study:
In this study, the investigators
used data from the ongoing Nurses’ Health
Studies, which are questionnaire-based series
that track risk factors of chronic diseases
in female nurses. They focused on 148 women
with MS who were enrolled in the study and
who had provided blood samples for the study,
and matched those cases with 296 nurses without
MS who had also given blood samples. Using
the samples of blood serum, they identified
those with HLA DR 15 genes, and also measured
for EBV antibodies. As in previous studies,
they found that having HLA DR15 genes increased
a person’s risk of MS from two to nearly
three times than those without the genes. Also
confirming previous findings, those with high
levels (four times the normal level) of EBV
antibodies had up to twice the risk of developing
MS. What was new in this study is that they
compared MS risks in those with both or neither
risk factor. They found that women with both
HLA DR15 and high levels of EBV antibodies
were nine times as likely to develop MS than
women who did not have the gene and had low
levels of antibodies.
Implications:
Further research is required
to confirm the findings from this relatively
small study, and to determine whether they
apply to other populations, including men.
Also, even if these risk factors combine to
increase some people’s risk of developing
MS, that risk is still quite small. However,
this approach is important because it looks
at the combined impact of risk factors in MS,
a complex disease that has thus far yielded
multiple and sometimes conflicting results
as to risk factors and how they might cause
the disease.
In an editorial accompanying this article,
Dr. Ruth Ann Marrie (University of Manitoba,
Winnipeg) comments on the importance of doing
studies like this one. She notes that one possible
reason why studies focusing on single risk
factors have been inconsistent in MS may be
that MS involves “multiple, interacting
risk factors from both the genetic and environmental
realms.” In line with this, one of the
top research priorities identified by a recent
National MS Society task force on the epidemiology
of MS are studies of the interactions between
MS genes and possible environmental triggers.
ASK MS Information System Code: 2.2.i
National Client Services
Medical Information and Education
Disponible
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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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