South Africans show genetic vulnerability to TB

Chest X-ray of a patient with TB Copyright: WHO/STB/Colors Magazine/J. Mollison

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[CAPE TOWN] South African blood samples have helped identify a new genetic link to people’s susceptibility to tuberculosis (TB). The research is published in this month’s issue of PLoS Medicine (January 2006).

It joins a growing body of research on genetic determinants of the disease, which kills two million people every year (see Single genetic change ‘can multiply TB risk by seven’).

Tuberculosis is caused by a bacterium that is so widespread in South Africa that most people have been exposed to it. Yet, only ten per cent of those infected develop the disease.

Researchers at South Africa’s Stellenbosch University spent years collecting blood samples from local communities.

Chantal Babb, a doctoral student, then took the samples to the Pasteur Institute in France to analyse the donors’ genetics with laboratory equipment not usually found in developing countries.

The study revealed that people who had been exposed to the virus but did not fall ill were more likely to have a variant of one particular gene than those who did become ill.

The gene produces a chemical called DC-SIGN, which is known to affect other diseases including HIV/AIDS, Ebola, hepatitis C and dengue fever. But, until now, variation in DC-SIGN had never been linked to TB.

“There is still much to learn and we feel genetics is very important at this stage,” says Eileen Hoal, who led the Stellenbosch team.

Van Helden warns that
a two-pronged approach
is needed to fight TB
Credit: (NSTF)

“We still don’t understand what happens when the [TB] bacteria gets into the person and the immune system kicks in with a variety of responses, some of which are successful, some of which work for a while and then break down, and some which don’t work at all, especially if they have HIV.”

“Ultimately, we need to help the patient’s immune system fight off the bacterium and not just target the bacterium with antibiotics,” says Paul van Helden, a member of the research team and director of Stellenbosch University’s Centre for Molecular and Cellular Biology.

He warns, however, that the findings will require years of further research before “useful implementation”, particularly because the TB bacterium is influenced by other factors.

Link to full paper in PLoS Medicine