Factor IX deficiency

Haemophilia B results from a congenital deficiency of Factor IX coagulant activity. It is an X-linked recessive disorder affecting 1 in 30 000 males.

It 'breeds' true so that family members tend to be all severely affected or all mildly affected.

It is clinically indistinguishable from haemophilia A, presenting with recurrent haemorrhage, spontaneously or post-operatively, into soft tissues and joints.

Hemophilia B is due to a defect in the F9 gene resulting in inadequate production of factor IX (1,2)

• genetic defect can occur either through X-linked inheritance or a spontaneous de novo mutation
• condition predominantly affects males, the carrier females may also occasionally experience more significant bleeding symptoms

The diagnosis of hemophilia B is established in a male proband by identification of decreased factor IX clotting activity (1,2)

• Severe hemophilia B. <1% factor IX clotting activity
• Moderate hemophilia B. 1%-5% factor IX clotting activity
• Mild hemophilia B. 6%-40% factor IX clotting activity

The normal range for factor IX clotting activity is approximately 50%-150% (2).

Reference:

1. Alshaikhli A, Killeen RB, Rokkam VR. Hemophilia B. [Updated 2023 Oct 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560792/
2. Konkle BA, Nakaya Fletcher S. Hemophilia B. 2000 Oct 2 [Updated 2024 Jun 6]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1495/