Patient's genes impact on malarial anemia severity
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Malarial Anemia Severity May Depend On The Patient's Genes
14 May 2006
http://www.medicalnewstoday.com/medicalnews.php?newsid=43294
Cell and animal studies conducted jointly by scientists at Johns Hopkins, Yale
and other institutions have uncovered at least one important contributor to the
severe anemia that kills almost half of the 2 million people worldwide who die
each year of malaria. The culprit is a protein cells make in response to
inflammation called MIF, which appears to suppress red blood cell production in
people whose red blood cells already are infected by malaria parasites.
The parasite that causes malaria - known as plasmodium - is carried through
blood by mosquito bites, and in parts of the world where mosquitoes thrive,
millions are infected, most of them by early childhood. Once in the bloodstream,
plasmodium invades liver and red blood cells and makes more copies of itself.
Eventually, as red cells break and free plasmodium to infect other cells, and as
the body's immune system works to kill infected cells, the total number of red
blood cells drops, causing anemia.
But not everyone infected with malaria develops severe, lethal anemia. And there
are cases where patients who have been cured of infection still develop severe
anemia.
This report provides the rationale for a simple, genetic test to sort out which
children may be most susceptible to this lethal complication of malarial
infection and to identify treatments targeted to them especially, the study's
authors suggest.
"This is important because in places where malaria is endemic, drug treatment
resources are scarce," says the study's primary author, Michael A. McDevitt,
M.D., Ph.D., an assistant professor of medicine and hematology at the Johns
Hopkins School of Medicine.
"There are many difficulties with blood transfusion safety and access in Africa,
especially in rural areas where most of the malaria-related deaths occur," says
McDevitt. "That led us to search for a better way to identify those most at risk
and a better way to treat the disease," he says.
The study, published online April 24 in the Journal of Experimental Medicine,
adds to a growing amount of evidence that an individual's unique genetic makeup
can affect the prevalence and outcome of diseases, in this case the individual
risk of malarial anemia.
A number of human proteins, including MIF (which stands for migration inhibitory
factor), were long suspected to cause malarial anemia because they are known to
reduce red blood cell counts as part of the body's normal response to such
inflammatory conditions as rheumatoid arthritis or some cancers.
Using immature blood cell precursors grown in a dish, the research team showed
that adding MIF to the cells decreases both the final number and maturity of red
blood cells. The researchers believe this effect can lead to anemia.
When infected with plasmodium, mice genetically engineered to lack MIF
experience less severe anemia and are more likely to survive. Without MIF around
to prevent blood cells from maturing, the mice appear better able to maintain
their oxygen carrying capacity and don't lose as much hemoglobin, the protein
found in red blood cells responsible for binding to oxygen molecules.
"Demonstrating that MIF clearly contributes to severe anemia suggests new ideas
for therapies that can block MIF in malaria patients," says the study's senior
author, Richard Bucala, M.D., Ph.D., a professor of medicine at Yale University
School of Medicine.
The research team also found different versions of "promoter" DNA sequences next
to the MIF gene that control how much MIF protein a cell makes in response to
infection. One version of the MIF promoter leads to less MIF protein made, while
cells containing another version of the MIF promoter make much more MIF protein.
Differences in the MIF promoter also have been linked to the severity of other
inflammatory diseases.
The researchers continue to collaborate in an effort to develop drugs that might
block MIF and treat severe anemia in malaria patients.
The researchers were funded by the National Institutes of Health, the Office of
Research on Minority Health, a Howard University General Clinical Research
Center grant, and the Department of Medicine at Johns Hopkins.
Authors on the paper are McDevitt, Ganapathy Shanmugasundaram and Jeffrey Keefer
of Johns Hopkins; Jianlin Xie and Christine Metz of the Feinstein Institute for
Medical Research; Jason Griffith, Aihua Liu, Courtney McDonald, Lin Leng and
Bucala of Yale; Philip Thuma of the Macha Malaria Research Institute in Choma,
Zambia, a field unit of the Johns Hopkins Bloomberg School of Public Health;
Victor Gordeuk of Howard University; Robert Mitchell of the James Graham Brown
Cancer Center; and John David of Harvard School of Public Health.
On the Web:
http://www.jem.org/cgi/content/full/jem.2035iti1v1
Audrey Huang
mailto:audrey@jhmi.edu
Johns Hopkins Medical Institutions
http://www.hopkinsmedicine.org
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