Understanding Hemophilia: Inheritance, Mechanism & Management

Hemophilia is an X-linked recessive bleeding disorder caused by deficient clotting factor VIII (Hemophilia A) or IX (Hemophilia B). It does not “spread” like infection; it is inherited or arises de novo.

Genetics & Inheritance

• Gene location: F8 (Xq28) or F9 (Xq27.1).
• Males (XY): One mutated allele → disease. Severity correlates with residual factor activity (<1% severe, 1–5% moderate, >5% mild).
• Females (XX): Usually asymptomatic carriers (lyonization). Symptomatic if skewed X-inactivation, Turner syndrome, or homozygous.

Transmission Patterns

• Affected father → all daughters are carriers; no affected sons.
• Carrier mother → 50% sons affected, 50% daughters carriers.
• De novo mutations: ~30% of cases, no family history.

Pathophysiology

Factor VIII/IX deficiency impairs tenase complex (FIXa-FVIIIa) → reduced thrombin generation → unstable fibrin clot → delayed/recurrent bleeding, especially into joints (hemarthrosis) and muscles.

Management

• Factor replacement: Recombinant or plasma-derived FVIII/FIX; prophylactic (primary/secondary) or on-demand.
• Extended half-life products, emicizumab (bispecific antibody mimicking FVIIIa) for Hemophilia A with/without inhibitors.
• Gene therapy: Roctavian (valoctocogene roxaparvovec) for Hemophilia A; Hemgenix (etranacogene dezaparvovec) for Hemophilia B – emerging curative options.
• Comprehensive care: HTC (Hemophilia Treatment Center) multidisciplinary team; physiotherapy, dental, psychosocial support.

Family Planning

Genetic counseling, prenatal diagnosis (CVS/amniocentesis), preimplantation genetic testing (PGT-M) available.