Molecular genetic analysis of Korean patients with coagulation factor XII deficiency:

Mechanism, Functions, and Diagnostic Relevance of FXII Activation by Foreign Surfaces

Factor XII (FXII) is a serine protease zymogen produced by hepatocytes and secreted into plasma. The highly glycosylated coagulation protein consists of six domains and a proline-rich region that regulate activation and function. Activation of FXII results from a conformational change induced by binding ("contact") with negatively charged surfaces. The activated serine protease FXIIa drives both the proinflammatory kallikrein-kinin pathway and the procoagulant intrinsic coagulation cascade, respectively. Deficiency in FXII is associated with a prolonged activated partial thromboplastin time (aPTT) but not with an increased bleeding tendency. However, genetic or pharmacological deficiency impairs both arterial and venous thrombosis in experimental models. This review summarizes current knowledge of FXII structure, mechanisms of FXII contact activation, and the importance of FXII for diagnostic coagulation testing and thrombosis.

Genetic analysis of a pedigree with hereditary coagulation factor XII deficiency

The aim of this study was to elucidate the molecular defects of a Chinese family with hereditary coagulation factor XII (FXII) deficiency. The FXII activity (FXII:C) and FXII antigen (FXII:Ag) levels were measured by clotting assay and ELISA, respectively. To identify mutations, the F12 gene sequencing was carried out. ClustalX-2.1-win and four online bioinformatics tools were applied to study the conservatism and harm of the mutation. The proband's FXII:C and FXII:Ag were 3 and 4%, respectively. Sequencing analysis revealed compound heterozygous mutations, including the deletion mutation (c.130delG) resulting in p.E26Sfs∗50 and the missense mutation (c.1561G>A) resulting in p.E502K. Bioinformatics indicated that mutations probably disrupt the function of the FXII protein. The c.130delG heterozygous deletion variation and the c.1561G>A heterozygous missense variation were responsible for the reduction of FXII:C in this family, of which c.130delG was first reported in the world.

Compound heterozygous mutations Glu502Lys and Met527Thr of the FXII gene in a patient with factor XII deficiency

OBJECTIVE

To study the gene mutation of human coagulation factor XII (FXII) in a Chinese family with FXII deficiency and it will help us to understand the pathogenesis of this type of disease.

CLINICAL PRESENTATION

The proband was a 50-year-old male who had a fracture of the right humerus. The routine presurgical coagulation test showed a significant prolonged activated partial thromboplastin time (APTT) at 59.1s (reference range, 29.0-43.0s).

TECHNIQUES

FXII activity (FXII:C) and FXII antigen (FXII:Ag) were detected by the one-stage clotting method and ELISA, respectively. To identify mutations, the FXII whole exon and flanking sequences were carried out. Suspected mutations were confirmed by reverse sequencing. The conservatism and possible impact of the amino acid substitution were analyzed by ClustalX-2.1-win and four online bioinformatics tools.

RESULTS

Phenotypic analysis revealed the FXII:C and FXII:Ag of the proband were 4% and 5%, respectively (normal range, 72-113%). Gene sequencing detected compound heterozygous mutations c.1561G > A (Glu502Lys) and c.1637T > C (Met527Thr) in exon 13. Bioinformatics and model analysis indicated that mutations probably had disrupted the function and structure of the FXII protein.

CONCLUSION

We detected two missense mutations Glu502Lys and Met527Thr in the catalytic domain of the proband, of which Met527Thr was first reported in the world. Our findings suggest that the double mutations in the FXII gene were the causing reasons for the decreased FXII:C and FXII:Ag. These results not only enriched the F12 mutation database in this condition, but also helped to identify the genetic defects of FXII in China.

Improving Blood Plasma Glycoproteome Coverage by Coupling Ultracentrifugation Fractionation to Electrostatic Repulsion-Hydrophilic Interaction Chromatography Enrichment

Blood plasma is considered to be an excellent source of disease biomarkers because it contains proteins, lipids, metabolites, cell, and cell-derived extracellular vesicles from different cellular origins including diseased tissues. Most secretory and membranous proteins that can be found in plasma are glycoproteins; therefore, the plasma glycoproteome is one of the major subproteomes that is highly enriched with disease biomarkers. As a result, the glycoproteome has attracted much attention in clinical proteomic research. The modification of proteins with glycans regulates a wide range of functions in biology, but profiling plasma glycoproteins on a global scale has been hampered by the presence of low stoichiometry of glycoproteins in a complex high abundance plasma proteome background and lack of effective analytical technique. This study aims to improve plasma glycoproteome coverage using pig plasma as a model sample with a two-step strategy. The first step involves fractionation of the plasma proteins using ultracentrifugation into supernatant and pellet that is believed to contain low abundant glycoproteins. In the second step, further enrichment of glycopeptides was achieved in both fractions by adopting electrostatic repulsion hydrophilic interaction chromatography (ERLIC) coupled to tandem mass spectrometry (LC-MS/MS) analysis. The coverage of enriched glycoproteins in supernatant, pellet, and whole plasma sample as control was compared. Using this simple sample fractionation approach by ultracentrifugation and further ERLIC enrichment technique, sample complexity was reduced and glycoproteome coverage was significantly enhanced in supernatant and pellet fractions (by >50%) compared with whole plasma sample. This study showed that when ultracentrifugation is coupled to ERLIC glycopeptides enrichment and glycoproteome identification are significantly improved. This study demonstrates the combination of ultracentrifugation and ERLIC as a useful method for discovering plasma glycoprotein disease biomarkers.

Novel deleterious mutation in the F12 gene in a Korean family with severe coagulation factor XII deficiency

Coagulation factor XII (FXII) is involved in the initiation of blood coagulation, fibrinolysis, complement systems, and bradykinin generation. Hereditary deficiency of FXII is caused by mutations in the F12 gene. In this report, we describe a Korean family with severe FXII deficiency from F12 mutations. The proband was a 46-year-old woman and was shown to have a markedly prolonged activated partial thromboplastin time at 126.7 s (reference range, 29-42 s) on routine health checkup. She had no history of bleeding tendency. Complete correction of prolonged activated partial thromboplastin time on mixing test prompted us to perform factor assays, which revealed a markedly decreased FXII activity (<0.5%; below the detection limit). Direct sequencing analyses for F12 showed that the proband was compound heterozygous for two deleterious mutations, c.249delG (p.Q83HfsX12) and c.405C>A (p.C135X). Family study showed that her sister with prolonged activated partial thromboplastin time at 83.8 s and FXII activity less than 0.5% was also compound heterozygous for the mutations. Q83HfsX12 was a novel frameshift mutation in exon 4 of F12, and C135X is a nonsense mutation previously reported in a Korean patient who was homozygous for the mutation. Thus, the C135X mutation is a recurrent mutation in Korean individuals with FXII deficiency, potentially with a founder effect.