Hemophilia, a blood clotting disorder caused by a mutation on the X chromosome, can be passed along the maternal line within families; men are more likely to develop it, while women are usually carriers. Sufferers can bleed excessively, since their blood does not properly coagulate, leading to extreme pain and even death. Victorias son Leopold, Duke of Albany, died from blood loss after he slipped and fell; her grandson Friedrich bled to death at age 2, while two other grandsons, Leopold and Maurice, died of the affliction in their early 30s. As Victorias descendants married into royal families throughout the Europe, the disease spread from Britain to the nobility of ?Germany, Russia and ?Spain. Recent research involving DNA analysis on the bones of the last Russian royal family, the Romanovs (who were executed in 1918 after the Bolshevik Revolution) revealed that Victorias descendants suffered from a subtype of the disorder, hemophilia B, which is far less common than hemophilia A and now appears to be extinct in the European royal lines.