Hemophilia A, B & C: The Three Different Clotting Factor Deficiencies

The two most common types of hemophilia are factor VIII deficiency (hemophilia A) and factor IX deficiency (hemophilia B, or Christmas disease).

Hemophilia A and hemophilia B are inherited conditions and considered rare diseases by the National Institutes of Health. A rare disease is one that affects fewer than 200,000 individuals in the United States. Both hemophilia A and B affect all races and ethnic groups equally.

Hemophilia A is most common. It occurs in about one in 5,000 male births; annually about 400 babies are born with hemophilia A.

Hemophilia B is the second most common type of hemophilia. Hemophilia B occurs in about one in 25,000 male births and affects about 3,300 people in the United States.

According to the US Centers for Disease Control and Prevention, the exact number of people living with hemophilia in the United States is not known, although researchers currently estimate it to be about 20,000.

Hemophilia A and B are the best known types of hemophilia, but other clotting factor deficiencies also exist. Hemophilia C, also known as Rosenthal syndrome, is caused by low levels of factor XI (11), another blood protein required to make a blood clot. Although associated with bleeding, hemophilia C differs from hemophilia A and B in cause and bleeding tendency.