Factor XII Deficiency
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Clinical Features of Factor XII Deficiency
Factor XII deficiency was first described in 1955 and initially named Hageman factor deficiency after the name of the index case (index case is the first individual identified with a particular phenotype). The original cases were described as having markedly prolonged clotting times. The frequency of factor XII deficiency is unknown as individuals carrying mutations in the gene can lack associated symptoms. At least 10 different mutations have been described in the factor XII gene. The symptoms of factor XII deficiency do not manifest with spontaneous or post-surgical bleeding but rather are diagnosed when an incidental activated partial thromboplastin time (aPTT) is markedly prolonged in an otherwise asymptomatic patient. The aPTT is a test used to measure the performance of both the intrinsic and extrinsic coagulation cascades. A definitive diagnosis of factor XII deficiency is accomplished by a modified aPTT using factor XII-deficient plasma.
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Michael W. King, Ph.D / IU School of Medicine / miking at iupui.edu