Kidney stones afflict millions of people worldwide every year, triggering a crippling pain that is among the worst known to man. Now, scientists at the Washington University School of Medicine in St. Louis have figured out why some people develop the condition more than others, potentially opening the way to more effective treatments. “We finally have a more complete picture detailing why some people develop kidney stones and others do not,” Jianghui Hou, a senior study author and assistant professor of medicine at Washington, reports the journal of European Molecular Biology Organization. Because kidneys function the same way in mice as in humans, the new findings can help scientists understand the root causes of kidney stones in patients, says a university statement. Most kidney stones form when the urine becomes too concentrated, allowing minerals like calcium to crystallize and stick together. Diet plays a role in the condition—not drinking enough water or eating too much salt (which binds to calcium) also increases the risk of stones. But genes are partly to blame. A common genetic variation in a gene called claudin-14 recently has been linked to a substantial increase in risk—roughly 65 percent—of getting kidney stones.