Severe hemophilia A is a subtype of hemophilia A defined by a profound deficiency of clotting factor VIII, resulting in frequent spontaneous hemorrhage and excessive bleeding following minor injuries, surgery, or dental procedures. The condition affects approximately 1 to 9 individuals per 100,000 people and is recognized by Orphanet and GARD as a distinct clinical entity.

The hallmark of severe hemophilia A is recurrent and often spontaneous bleeding, particularly into joints, muscles, and soft tissues. Excessive hemorrhage following surgery, tooth extraction, or minor trauma is characteristic. Repeated joint bleeds may contribute to progressive joint damage over time. Central nervous system bleeding represents a serious potential complication.

Severe hemophilia A is characterized by markedly reduced activity of clotting factor VIII, central to the normal coagulation cascade. Specific genetic data for this condition were not certified in the known_genes field of this packet. No inheritance pattern data were documented.

Diagnosis relies on laboratory measurement of factor VIII activity levels; severe hemophilia A is defined by very low or undetectable factor VIII activity. Assessment for inhibitory antibodies against factor VIII is conducted as part of diagnostic evaluation, as inhibitor presence has significant implications for management.

Marstacimab-hncq (Hympavzi), a subcutaneous bispecific antibody targeting the tissue factor pathway inhibitor, is documented in this packet as having received approval for routine prophylaxis to prevent or reduce bleeding in individuals with hemophilia A, with or without inhibitors. Additional investigational biologics and gene therapy candidates are under active clinical development, including several designated orphan drug candidates.

Specific prognosis data for severe hemophilia A were not certified in this packet. The condition is associated with a high burden of spontaneous bleeding and risk for chronic joint complications. Individual outcomes vary based on inhibitor status and access to appropriate interventions.

Severe hemophilia A is an active research area with numerous ongoing clinical trials. Active studies include a Phase 3 gene therapy trial of giroctocogene fitelparvovec (NCT04370054, Pfizer, estimated completion October 2026), a Phase 3 pediatric study of marstacimab (NCT05611801, Pfizer, recruiting), and a Phase 1 gene therapy study of SPK-8011QQ (NCT07226206, Hoffmann-La Roche, recruiting). Published research includes 202 classified articles with gene therapy and clinical trial publications well represented.