08 December 2009

Genes may shield some from TB

A study has identified genetic traits that may protect some people from tuberculosis in a finding that could help lead to a new TB vaccine, scientists said.


A study involving 128 South African families has identified genetic traits that may protect some people from tuberculosis in a finding that could help lead to a new TB vaccine, scientists said.

Tuberculosis is the world's seventh-leading cause of death, killing 1.8 million people worldwide in 2008, about half a million of whom also had Aids.

The study, published in the Journal of Experimental Medicine, could help reveal mechanisms behind natural resistance against TB infection, researchers said.

"The take-home message is that to be infected or not infected is not a matter of luck. To be infected or uninfected is a characteristic of individuals and therefore can be manipulated to prevent infection," said Erwin Schurr, molecular geneticist at McGill University's Department of Human Genetics in Canada who led the study.

"There are, in fact, big advantages because if it is in your genome, it means these are factors you can identify. Once you identify them, you can target them in people who are actually prone to infection," Schurr said. 

How the study was done

A better vaccine is needed against TB. The Bacille Calmette-Guerin (BCG) vaccine to prevent TB has been around since 1919, but it gives only some measure of protection for children and does not protect adults.

TBis caused by a bacterium called Mycobacterium tuberculosis, and it typically attacks the lungs. Schurr and his colleagues studied 128 families living in two Cape Town suburbs where tuberculosis has a high prevalence.

No one in the families was sick with TB, although some were infected by the TB bacterium. Those families included 186 parents and 350 offspring. Among the children, the researchers found that about 40% of them were uninfected by the bacterium.

After studying the genes of the people in the study, the scientists detected genetic patterns among children who were infected with TB and those who were not, particularly relating to two specific chromosomes.

"We found chromosome 11 and chromosome five that were enriched in particular children (who were uninfected)," Schurr said."We need to enrol additional participants in Vietnam and Morocco, in addition to South Africa," Schurr said.

Gene to be cloned

He added that the researchers will clone the genes that appear to provide protection, then do studies to try to figure out how the genes led to the resistance.

"And the next step is you learn how to interfere in that function in people who are susceptible (to TB)."The team hopes the findings can lead to a better vaccine. TB spreads very easily through the air when people who are sick with TB cough, sneeze, talk or spit.

One out of every three people in the world is infected with the bacteria, but most of these are "latent infections" and carriers show no symptoms and are not infectious. However, one in 10 will become sick with active TB in his or her lifetime due primarily to a weakened immune system.

The UN World Health Organisation estimates that 9.4 million people developed active TB in 2008. - (Reuters Health, December 2009)


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