These are a group of genetic disorders characterized by a deficiency of one of the coagulation pathway factors.

Haemophilia A is characterized by a deficiency of one subunit of factor VIII (factor VIII C).

Haemophilia B is the result of a deficiency of factor IX.

Von Willebrand's disease is a result of a variable deficiency of subunits of factor VIII (factor VIII RAG and factor VIII RiCoF) with a relatively normal factor VIII C level.