Every year leprosy strikes nearly 700,000 people, causing devastating nerve damage, sensory loss and disfiguration. But a new analysis of the leprosy bacterium's genome, published today in the journal Nature, is providing fresh insight into the microbe's mysterious ways. The results could eventually lead to better ways for diagnosing and treating the disease.

Stephen T. Cole of the Pasteur Institute in Paris and his colleagues compared the gene sequence of the leprosy bacterium, Mycobacterium leprae, with that of the tuberculosis bacterium, M. tuberculosis, a close relative. Intriguingly, they found that M. leprae has undergone a major reductive evolution. That is, it has lost a large number of genes--so many, in fact, that it now has only the bare minimum necessary for survival. Because many of the lost genes were involved in metabolism, the organism divides slowly, which, combined with the fact that its nutrient requirements continue to elude researchers, has made growing it in the lab quite difficult. But with relatively few genes to wade through, scientists will now have an easier time identifying the important ones.

Knowing M. leprae's sequence should help researchers to identify molecular drug targets--products of the remaining few genes involved in metabolism, for example--as well as proteins that could enable the development of new diagnostic tests for the disease. The new study may likewise benefit efforts to develop novel drugs and vaccines for tuberculosis