Synonym: Christmas disease
Haemophilia B is due to a deficiency of clotting factor IX (haemophilia A is due to a deficiency of clotting factor VIII). They are both X-linked recessive conditions. By and large, haemophilia B tends to be similar to haemophilia A but less severe.
This is a companion discussion topic for the original article at https://patient.info/doctor/haematology/haemophilia-b-factor-ix-deficiency