Now
virtually all the same genes,
has only a one in four chance
of developing the disease,
suggesting that factors other
than genetics are involved.
Another reason is that data
from epidemiological studies
(studies that analyze the
geographical, socioeconomic,
genetic and other factors that
may contribute to who gets
MS) suggest that exposure to an
infectious agent may be involved
in triggering the disease. And
immune system proteins that
are typically found in the spinal
fluid of people with nervous
system diseases that are known
to be reactions to viruses are
also found in the spinal fluid
of 90 to 95 percent of people
with MS.
That said, researchers have
yet to pinpoint a single virus
as the trigger for MS. Several
viruses have been studied, but
proving a cause-and-effect
relationship between any virus
and MS requires many research
steps. One of these steps is to
show that the virus is in the
body before MS develops. We
also need to show—and this is
the most difficult step—that the
virus actually causes the disease,
and is not just happening
alongside the disease.
Certainly, the virus that has
come the longest way on this
road is the Epstein-Barr virus.
The case for Epstein-Barr
Epstein-Barr virus (EBV) is
known to cause infectious
mononucleosis and other
disorders. Most everyone has
been exposed to EBV, though
not everyone develops an illness
from it. Key studies from
Alberto Ascherio, MD, DrPH,
and his team at the Harvard
School of Public Health, have
made EBV the front-runner for
a virus involved in MS.
• Dr. Ascherio and colleagues
examined stored blood
serum samples that had
been collected from several
large groups of individuals
who were then followed
for the occurrence of MS.
Antibodies (immune proteins
that indicate a person has
been exposed) to EBV
were significantly higher
in people who eventually
developed MS than in control
samples of people who did
not get the disease (JAMA
2001; 386:3083; JAMA
2005;293:2496; Archives of
Neurology 2006;63:839).
JILL K. GREGORY
