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At a glance

Inherited coagulation disorder caused by a deficiency in plasma protein factor XII (FXII) characterized by in vitro delayed blood clotting without a clinical bleeding tendency. The condition may also be acquired and temporary.

Synonyms

Factor XII Deficiency; HAF Deficiency; Hageman Trait; Coagulation Factor XII.

History

Hageman factor was first discovered in 1955 when a routine preoperative blood sample of the 37-year-old railroad brakeman John Hageman (1918) was found to have prolonged clotting time without a history of hemorrhagic symptoms. Oscar Ratnoff, a hematologist, found that Hageman lacked a previously unidentified clotting factor. Ratnoff later found that the Hageman factor deficiency was autosomal recessive.

Incidence

From 1955 to 2002, only a few hundred reported cases. Incidence is greater in patients of Asian origin.

Genetic inheritance

Autosomal recessive. Location of the Hageman factor gene was difficult; it was successively assigned to chromosome 6 and then 7, and now the gene map locus has been established as 5q33-ter. Human Factor XII is 596 amino acids long. The heavy chain (353 residues) and a light chain (243 residues) are held together by a disulfide bond. It is 80,000 daltons.

Pathophysiology

FXII is a contact factor belonging to the kallikrein-kinin system or plasma. Patients affected with a deficiency in FXII do not experience abnormal bleeding because there is activation by other contact factors. The diagnosis is usually serendipitous. Partial thromboplastin time is elevated.

Diagnosis

Prolonged partial thromboplastin time; considerably decreased FXII assay. Condition usually discovered during routine laboratory examination. Unlike other clotting factor deficiencies, factor XII deficiency is totally asymptomatic and does not cause excess bleeding. Factor XII does play an important role in clot formation.

Clinical aspects

Elevated partial thromboplastin time, no clinical bleeding in normal conditions. Occasionally, mild blood loss has been reported, mainly following trauma or surgery. Severe liver disease may lead to reduced production of FXII, worsening the (biologic) condition. FXII deficiency was reported to be a risk factor for thromboembolism as a result of inactivation of fibrinolysis. The disorder may be a risk factor for early gestational losses.

Precautions before anesthesia

Evaluate the coagulation profile and specific dosage of clotting factors. Even when partial thromboplastin time is considerably prolonged, there is no indication for fresh-frozen plasma, and common surgical procedures should not be contraindicated. These patients are not prone to develop a bleeding tendency but, on the contrary, might be at risk for thromboembolism (spontaneously and perioperatively).

Anesthetic considerations

Classically, there are no specific contraindications to anesthesia. However, bleeding problems may arise in procedures requiring use of anticoagulants (cardiac surgery), requiring close followup of both global coagulation ...

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