5
per 100,000
Prevalence
of MS in
Nigeria
15
per 100,000
Prevalence
of MS in
Tunisia
100
per 100,000
Prevalence
of MS in
Sweden
Sunlight may cut
MS risk by itself
Study complicates theories
about the role of vitamin D
By Nathan Seppa
Ultraviolet radiation from the sun seems
to thwart multiple sclerosis, but perhaps not the way most researchers had
assumed, a new study in mice suggests.
If validated in further research, the
finding could add a twist to a hypothesis that has gained credence in recent
decades. The report appeared online
March 22 in the Proceedings of the
National Academy of Sciences.
Scientists have observed that MS is rare
in the tropics and more common at high
latitudes, presumably because people living nearer the equator synthesize more
vitamin D thanks to more sun exposure.
But a direct cause-and-effect relationship between vitamin D deficiency
and MS has never been established. In
recent mouse experiments, biochemist
Hector DeLuca and his team at the University of Wisconsin–Madison tested
the link between vitamin D and MS risk
and came away unconvinced.
In MS, the immune system attacks fatty
myelin sheaths that insulate
nerves. DeLuca and his team
induced a condition comparable to human MS in mice
by injecting the animals with
proteins that instigate similar myelin damage.
The researchers exposed
some mice to UV light
before and after giving
the animals the damaging
injection. Another group of mice got the
injection but not the UV exposure.
The mice exposed to UV suppressed
the MS-like disease better than the con-
trol mice, the researchers found, even
though the UV radiation dose wasn’t
enough to greatly increase the animals’
blood concentrations of vitamin D.
In another test, the scientists gave the
mice varying doses of vitamin D supplements, but did not expose the animals to
UV light. At safe doses, the supplements
failed to control the disease.
“We concluded that UV
light is doing something
beyond” making vitamin D,
DeLuca says.
Multiple sclerosis risk
might well be influenced
by a biological mechanism
apart from vitamin D blood
levels, but many questions
remain, including how UV
radiation might inhibit the
immune system and the development
of the disease, says George Ebers, a
neurologist at the University of Oxford
in England.
“We concluded
that UV light
is doing
something
beyond”
making
vitamin D.
HECTOR DELUCA
Identical twins differ at gut level
By Laura Sanders
Twins may share appearances, mannerisms, even clothes — but the microbes in
their intestines are far from the same. By
cataloging microbial genes in the gut,
researchers have found that communities of bacteria can differ dramatically
even between identical twins.
The findings, which appeared online
April 2 in the Proceedings of the National
Academy of Sciences, give scientists a
deeper understanding of what makes
one person’s intestinal menagerie different from another’s.
Working out what’s behind the com-
position and function of a person’s gut
bacteria is “a very important problem,”
says microbiologist Frederic Bushman
of the University of Pennsylvania School
of Medicine in Philadelphia. Intestinal
bacteria spur digestion, manufacture
vitamins and keep people healthy;
changes in the bugs have been linked to
irritable bowel syndrome and metabolic
disorders. Because of their role in pro-
cessing the nutrients from food, gut bac-
teria may even influence body weight.
Only about 17 percent of DNA
sequences in the twins’ gut microbes
overlapped, based on a classification
scheme developed by the researchers.
What’s more, about 64 percent of the
gene groups identified had not been seen
in previous studies.
One of the notable differences between
the twins was a gene group that produces
proteins in a family called dockerins,
which form assemblies that microbes use
to break down cellulose. Only one twin’s
intestinal bacteria possessed these genes.
In addition to looking for which genes
were present in the gut microbiomes, the
team went a step further and determined
which ones were active. Some microbial
genes found in both twins showed similar levels of activity, but the researchers
found differences, too.
“This is the first look at the repertoire
of expressed genes,” Gordon says. The
results provide a baseline for understanding how gut microbe genes function differently in different people. s
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April 24, 2010 | science news | 9
