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Congenital factor XII (FXII) dexFB01;ciency is a rare autosomal recessive disorder, characterized by a great variability in its clinical manifestations. In this study, we screened for mutations in the F12 gene of 4 unrelated patients with FXII coagulant activity <10% of that of normal human plasma. To investigate the molecular defects in these FXII-deficient patients, we performed FXII mutation screening. By sequencing all coding exons as well as xFB02;anking intronic regions of the F12 gene, 6 different mutations, including 3 missense mutations (Gly341Arg, Glu502Lys and Gly542 Ser), 1 insertion (7142insertC) and 2 deletions (5741-5742 delCA and 6753-6755delACA), were identixFB01;ed on the F12 gene. Three of them (Gly341Arg, 5741-5742delCA and 6753-6755delACA) are reported here for the first time. Computer-based algorithms predicted these missense mutations to be deleterious. This study has increased our knowledge of the mutational spectrum underlying FXII deficiency.

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OBJECTIVE: To identify potential mutation underlying hereditary coagulation factor XII (FXII) deficiency in a pedigree and explore its molecular pathogenesis. METHODS: Activated partial thromboplastin time (APTT), FXII activity (FXII:C) and FXII antigen(FXII:Ag) and other coagulant parameters of the proband and 5 family members were measured. Potential mutations in the 14 exons and intron-exon boundaries of the FXII gene were screened with polymerase chain reaction (PCR) and direct DNA sequencing. Suspected mutations were confirmed with reverse sequencing. Corresponding PCR fragments from other family members were also sequenced. RESULTS: APPT of the proband and his son were significantly prolonged to 121.5 s and 98.5 s, respectively. FXII:C and FXII:Ag of the proband and his son have reduced to 5%, 6.8% and 9%, 12.2%, respectively. Plasma plasminogen activity (PLG:A) in both individuals was slightly higher than the normal reference range. FXII:C of his second daughter and grandson were slightly reduced to 64% and 60%. FXII:C of the other family members were all in the normal range (72%-113%). A heterozygous missense mutation, g.8597G>A, was identified in exon 13 of the FXII gene in the proband, which resulted in an p.Asp538Asn substitution. For the promoter regions of the FXII gene, the genotype of the proband was 46TT. The same mutations and 46T/T were also found in the proband's son but not in other members of the family. The genotypes of the proband's spouse, eldest daughter and grandson were 46CT, and his second daughter was 46TT. CONCLUSION: The heterozygous mutation of g.8597G>A identified in exon 13 of FXII gene is a novel mutation. Heterozygous p.Asp538Asn mutation and 46TT in the FXII gene can cause hereditary FXII deficiency, which was probably responsible for the low FXII concentrations in this pedigree.

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OBJECTIVE: To investigate the prevalence and clinical significance of congenital factor XII (FXII) deficiency in the South-European Caucasian (Greek) population in a cohort of women with recurrent spontaneous abortions (RSAs). STUDY DESIGN: One hundred women with a history of > or =2 RSAs of unexplained nature were compared to 100 age-matched, healthy controls with no history of thrombotic disease or adverse pregnancy outcomes, regarding FXII activity. Women were included in the RSA group if they had normal coagulation parameters and no congenital or acquired thrombophilia. RESULTS: Fifteen of 100 women with RSA had reduced FXII activity, whereas all controls had normal FXII activity. FXII activity was significantly lower in the RSA than in the control group (median 100.5, range 10-150 vs. median 104.2, range 58.3-143.2, p < 0.016 by Mann-Whitney test). FXII activity was positively correlated with age in both the RSA and the control groups (r = +0.1, p = 0.04 and r = +0.04, p = 0.2, respectively), but this correlation reached statistical significance in the RSA group only. A negative correlation between FXII activity and the number of abortions in the RSA group was found (r = -0.2, p = 0.03). CONCLUSION: Congenital FXII deficiency is strongly associated with RSA in the Greek population.

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Factor XII (F.XII, Hageman factor) is one of the contact system factors which initiates an intrinsic coagulation pathway. But its definite role is still unclear, because many cases of severe F.XII deficiency experience thrombotic events instead of a bleeding problem. Moreover most of them are asymptomatic. There have only been a few reports of F.XII deficiency in Thailand. The author reports two cases of congenital F.XII deficiency in Thai children.

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A 63-year-old man with deficiency of congenital coagulation factor XII, was referred to our hospital for an operation of the hypopharynx cancer. The day before surgery under general anesthesia, fresh frozen plasma was administered to him with good response of APTT shortening from 397.0 to 36.4 seconds. During operation, bleeding tendency was controlled and fresh frozen plasma was administered. Total blood loss during the operation was 255 ml. During post-operative period, APTT was kept at an adequate level. The post-operative course was uneventful and he was discharged after the radiation and an adjuvant therapy.

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To further elucidate the debated role of hereditary FXII deficiency as a thrombophilic risk factor this follow-up study on 65 subjects out of 12 Swiss families was undertaken (follow-up: 6 yrs). Fifteen severely FXII deficient subjects (FXII:C < 1%), 35 partially FXII deficient subjects (FXII:C > or = 1-59%), 10 with normal FXII values (FXII:C > or = 70%), and 5 non-classifiable subjects (FXII:C > or = 60-69%) were reevaluated. Eight subjects (4 severely and 3 partially FXII deficient, 1 non-classifiable) were newly enrolled. Four instances of deep vein thrombosis, one superficial vein thrombosis and one myocardial infarction were noted in 2 out of 19 severely FXII deficient subjects during a total life-time period of 866.6 patient-years. In 38 partially FXII deficient subjects (1862.8 patient-years) one ischemic cerebrovascular stroke and one superficial vein thrombosis were recorded in 2 individuals. The 10 subjects with normal FXII values (498.2 patient-years) remained thrombosis-free. One superficial vein thrombosis occurred in an unclassifiable woman. None of the 3 different FXII gene defects revealed in our patients was specifically associated with thromboembolic complications. Kaplan-Meier analysis of thrombosis-free survival suggests that hereditary partial (and probably severe) FXII deficiency does not constitute a thrombophilic condition.

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In order to assess the clinical implications of hereditary F XII deficiency, all available members of Swiss families with F XII deficiency were investigated. Based on the F XII:C values and the family pedigree, the 74 subjects, aged 8-82 years, were classified as homozygotes/double heterozygotes for F XII deficiency (n = 18), as obligatory (n = 20) or possibly (n = 25) heterozygotes, respectively, and as normals (n = 11). None of the 18 subjects with F XII:C less than 0.01 U/ml and only one possibly heterozygous woman had an abnormal bleeding tendency, confirming the notion that Hageman trait generally does not result in a hemorrhagic diathesis. Two of the 18 subjects with severe F XII deficiency had suffered from venous thromboembolic disease at age less than 40 years. One heterozygous woman had a leg ulcer probably due to venous thrombosis. Thus, whereas homozygous F XII deficiency may be associated with an increased risk for venous thromboembolic disease, partial F XII deficiency is not, by itself, a strong risk factor for thrombosis. Whereas 17 of the 18 subjects with F XII:C less than 0.01 U/ml had no detectable F XII:Ag, one cross reacting material-positive F XII deficient subject (F XII:Ag = 0.11 U/ml) was identified. The dysfunctional F XII, present in this subject's plasma and tentatively called F XII Bern, is the fourth abnormal F XII molecule identified so far.

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The plasma protein FXII (Hageman factor) has been shown to be linked with the plasma defence systems of coagulation, fibrinolysis, kallikrein-kinin and complement. It can be activated by surface contact activation and in solution. Surface contact activation is a complex phenomenon involving negatively charged surfaces, FXII, high molecular weight kininogen and plasma kallikrein. Fluid-phase activation can be effected by a variety of serine proteases. In both types of activation the FXII zymogen is converted to active enzymes. FXII levels in plasma are low or undetectable in both inherited deficiencies and in a variety of clinical conditions. FXII levels can also be elevated in some clinical conditions. Although discovered as a clotting protein FXII appears to play an important role in the kallikrein-kinin and fibrinolytic systems and also has effects on cells. Recent studies suggest that therapeutic blockade of activation of FXII can be of benefit in certain clinical conditions.

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The fortuitous detection of an increased activated cephalin clotting time is often dependent on defects of the blood-clotting factors synthesized by the liver, haemophilia or von Willebrand's disease, circulating anticoagulants or specific deficiencies of various factors necessary for blood-clotting mechanisms. Much more rarely, it may be due to an isolated Hageman factor defect. This deficiency does not lead to an increased bleeding tendency and surgery has proved surprisingly uneventful. On the other hand, thromboembolic events may appear. Being and inherited disease with autosomal recessive transmission, the discovery of Hageman factor deficiency must lead to a complete family investigation.

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Kallicrein (K) and prekallicrein (PK) were assayed in a large number of cases with congenitial clotting factor defects. Patients with factor XII deficiency were separated from other clotting abnormalities. The results were compared with a control group of normal subjects. We found significantly reduced PK activity levels in the factor XII deficient group. Although less evident, the reduction of PK activity in the group of other clotting defects was modest, however, not due to a factor VII defect. In our study we found that in the absence of factor XII, PK is not activated. Further studies will be necessary to show if PK activation is altered or reduced in other congenital clotting abnormalities.

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Platelet adhesiveness and aggregation were studied in two patients with congenital factor XI deficiency and in a patient with congenital factor XII deficiency. A normal aggregation pattern was observed in every instance, regardless of the aggregating agent. The same was true for platelet adhesiveness. It is concluded that factor XI and factor XII play no role in platelet aggregation and adhesiveness.

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