What do Emily Dickinson, Karl Marx, and Jesus of Nazareth have in common? They’ve all played a part in a popular parlor game. Retrospective diagnoses—thought experiments in which modern scientists use present-day diagnostic frameworks to suss out potential causes of historical disease and death—are a favorite game of would-be time travelers and a staple of medical conferences. The theories can range from plausible to wacky (Julius Caesar had epilepsy! No, wait—mini-strokes!). But until now, none have relied on DNA from the historical figures they were trying to diagnose.

Thanks to a particularly violent murder, however, researchers think they have solved a medical mystery that vexed a notorious French revolutionary. To do so, they analyzed DNA from the 200-year-old