An "immunity gene" evolved in populations across Southeast Asia 50,000 years ago to combat leprosy, a new study finds, and 110 million people of Southeast Asian descent carry the gene today.

What it matters: Leprosy still exists — there were 210,000 new cases reported worldwide in 2015. This study could help emerging gene therapy research combat remaining leprosy cases by further exploring the "immunity gene."

How it evolved: Leprosy is a chronic infection of the skin and peripheral nerves. The study, from Cell Reports, showed that a gene mutation produces proteins that bind to molecules from the bacterium that causes leprosy then shows it to the immune system, which destroys the infected cells. The mutation became more common in populations as it conferred protection from the disease.