What Are Rare Bleeding Disorders? In the US, a rare disease or disorder is defined as one that affects fewer than 200,000 people. This means hemophilia A and B, and the less-common factor deficiencies such as I, II, V, VII, X, XI, XII and XIII, are all rare disorders. Blood clotting is a complex process, involving many different proteins, called factors, each of which plays a different role in the blood clotting process. Factor deficiencies are defined by which specific clotting protein in the blood protein is low, missing or doesn't work properly. These very rare factor deficiencies were all discovered and identified in the 20th century. The majority of these conditions were only identified within the last 60-70 years.

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