Christmas disease, also otherwise known as hemophilia B, is an inherited deficiency of Factor IX, a plasma protein active in the formation of blood clots. The condition has the same
symptoms as classic hemophilia (hemophilia A), prolonged bleeding from
slight injuries and internal bleeding without any known cause. Christmas
disease is usually less severe than classic hemophilia; its severity is
dependent on the extent of the plasma protein deficiency. Transfusion of Factor IX concentrate is the appropriate treatment.
too much information: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?306900