A large part of the population carries a genetic mutation that increases the risk of developing tuberculosis.
1.7 million people died of TB worldwide in 2016. More than a quarter of them were children. The disease is caused by bacteria that are spread by coughing, sneezing and spitting. Researchers at Rockefeller University in the United States have discovered a genetic mutation that increases the risk of developing the disease. Another genetic variation is responsible for immune deficiencies that prevent the body from fighting certain mycobacteria.
The researchers wanted to understand why some people were more likely to get TB. They retrieved DNA extracts from TB patients and then performed analyzes. These show that the risk of having the disease is higher in patients who have two copies of a genetic variation linked to the TYK2 enzyme. Scientists have found that this genetic mutation is widespread: it is present in one in 600 people in Europe, and in the rest of the world, it affects between one in 1000 and one in 10,000 people.
Since the disease is rare today and concentrated in certain parts of the world, such as India, China or Indonesia, it is unlikely that people with this genetic mutation will ever contract TB. This discovery could, however, allow tests to be developed to warn travelers traveling to contaminated areas.
The group of researchers is also interested in mycobacteria: the bacillus causing tuberculosis, mycobacterium tuberculosis, belongs to this category of microbes. These are bacteria that are everywhere in the environment and are usually harmless. Some people are exceptions: those with a Mendelian predisposition to mycobacterial infections.
The researchers also found the tuberculosis is linked in fact to two genetic mutations, one leading to a deficiency of the IL-23 protein receptor, the other to a deficiency of the IL-12 protein receptor. These two proteins produce a molecule that allows the immune system to act against mycobacterial infections, so when people have this genetic variation, this molecule is not manufactured, and they get sick more easily. For the researchers, this discovery could improve treatments for this disease, but also better prevent the onset of tuberculosis.