title: Discordant identical twins. Christmas disease.
mesh_terms: D002675:Child, Preschool; D002869:Chromosome Aberrations / Q000235:genetics; D025063:Chromosome Disorders; D004200:Diseases in Twins; D005260:Female; D002836:Hemophilia B / Q000175:diagnosis / Q000235:genetics*; D006801:Humans; D010375:Pedigree