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A boy has clinical features identical to hemophilia A, but factor VIII is normal. Factor IX is deficient.
XLR; F9 (factor IX)
- Clinically indistinguishable from hemophilia A
- Factor IX deficiency
- 15% of hemophilia cases
- Prolonged aPTT with normal PT and a correcting mixing study, identical to hemophilia A
- Reduced factor IX activity assay (with normal factor VIII) distinguishes hemophilia B from hemophilia A and grades severity
- F9 sequencing confirms the diagnosis, enables carrier testing of at-risk females, and supports prenatal diagnosis
- Factor IX replacement, gene therapy