Congenital factor XII deficiency

Congenital factor XII deficiency, also known as Hageman factor deficiency, is a rare inherited disorder of the coagulation system caused by a deficiency or dysfunction of coagulation factor XII (FXII, Hageman factor). Factor XII is a serine protease that plays a role in the contact activation pathway of blood coagulation. The condition is caused by mutations in the F12 gene located on chromosome 5q35. Despite its role in the intrinsic coagulation cascade, factor XII deficiency is characteristically associated with a markedly prolonged activated partial thromboplastin time (aPTT) in laboratory testing but does NOT cause a clinical bleeding tendency. This is a key distinguishing feature of the condition. Paradoxically, some individuals with factor XII deficiency may actually have an increased risk of thromboembolic events, although this association remains debated in the medical literature. The condition was first described in John Hageman, a railroad worker who was incidentally found to have a prolonged clotting time but had no bleeding symptoms. Most individuals with factor XII deficiency are asymptomatic and are identified incidentally during routine preoperative coagulation screening or other laboratory evaluations. Homozygous or compound heterozygous individuals typically have very low or undetectable factor XII levels, while heterozygous carriers may have moderately reduced levels. No specific treatment is required for congenital factor XII deficiency, as the condition does not cause bleeding complications. Importantly, patients should be counseled that despite their abnormal laboratory coagulation results, they are not at increased risk of surgical or traumatic bleeding, and factor replacement therapy is not indicated. Patients should carry documentation of their diagnosis to avoid unnecessary delays in surgical procedures or inappropriate administration of blood products based on the prolonged aPTT finding alone. Genetic counseling may be offered to affected families.

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