Severe hemophilia A

Severe hemophilia A is the most serious form of hemophilia A (also known as factor VIII deficiency or classic hemophilia), a hereditary bleeding disorder caused by a deficiency or dysfunction of coagulation factor VIII (FVIII). In severe hemophilia A, factor VIII activity levels are less than 1% of normal (<0.01 IU/mL). The condition primarily affects the blood's ability to clot, leading to prolonged and often spontaneous bleeding episodes. It is caused by pathogenic variants in the F8 gene located on the X chromosome, and predominantly affects males, while females are typically carriers who may occasionally experience mild bleeding symptoms. The hallmark of severe hemophilia A is spontaneous bleeding, particularly into joints (hemarthroses) and muscles, which can begin in infancy or early childhood, often when the child starts crawling or walking. Recurrent joint bleeds most commonly affect the knees, elbows, and ankles, and can lead to chronic hemophilic arthropathy — a debilitating condition characterized by progressive joint destruction, chronic pain, and disability. Other serious manifestations include intracranial hemorrhage (which can occur even in neonates), prolonged bleeding after trauma or surgery, mucosal bleeding, hematuria, and gastrointestinal hemorrhage. Excessive bruising is often one of the earliest signs noticed by parents. Treatment for severe hemophilia A has evolved significantly. The standard of care includes prophylactic replacement therapy with plasma-derived or recombinant factor VIII concentrates, administered regularly to prevent spontaneous bleeding episodes and joint damage. Extended half-life FVIII products have reduced the frequency of infusions needed. Emicizumab, a bispecific monoclonal antibody that mimics the cofactor function of factor VIII, represents a major therapeutic advance and is administered subcutaneously, offering effective prophylaxis for patients both with and without inhibitors. A significant complication is the development of neutralizing antibodies (inhibitors) against factor VIII, which occurs in approximately 25–30% of patients with severe hemophilia A and complicates treatment. Immune tolerance induction therapy is used to eradicate inhibitors. Gene therapy using adeno-associated viral vectors has recently emerged as a potential transformative treatment, with valoctocogene roxaparvovec receiving regulatory approval, offering the possibility of sustained endogenous FVIII production.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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