Once known as the Royal Disease, hemophilia B is a rare bleeding disorder that stems from a defect in a specific clotting factor: factor IX. Factor IX, or F9, is a specialized protein needed in the coagulation cascade and the formation of a stable fibrin clot. Hemophilia B was once called the Royal Disease because Queen Victoria of England passed the factor IX mutation through several royal families in Europe. It is inherited in a recessive, X-linked fashion. Because of its mode of inheritance, males are primarily affected and become symptomatic, whereas females are mainly carriers. Queen Victorias eighth child, Prince Leopold, Duke of Albany, was a hemophiliac and died as a result of this disease at the age of 31. One may say that Queen Victoria was the Royal Diseases patient zero. Two of her five daughters, Alice and Beatrice, inherited the defective gene and became carriers like their mother. Beatrice passed it into the Spanish bloodline and Alice passed it into Russian and German bloodlines.