Phenotypic and genetic analyses of four cases of coagulation factor XII deficiency

Objectives: To identify the clinical phenotypic and molecular pathogeneses of four cases of coagulation factor XII deficiency and to deepen the cognition of this disease. Methods: Coagulation tests were performed through one stage of coagulation on a STAGO coagulation analyser. Coagulation factor XII antigen was detected using enzyme-linked immunosorbent assay. The species conservatism and structural change of mutant proteins were analysed using MegAlign and PYMOL. Meanwhile, missense variants and a novel splice site variant were identified using PolyPhen2 and NetGene2. Results: The four cases had an observably prolonged activated partial thromboplastin time but without obvious bleeding tendency. Their coagulation factor XII activity (FXII:C) and antigen (FXII:Ag) were greatly reduced. Six mutations were detected: NM_000505.4:c.3981G>A, NP_000496.2:p.(Pro182Leu), NP_000496.2:p.(Ser479Ter), NP_000496.2:p.(Cys559Arg), NC_000005.10:g.7217_7221delinsGTCTA and NM_000505.4:c.1681-1G>A. The first five are newly discovered mutations. The two missense mutation sites were highly conservative, and their protein secondary structure changes may occur not only on the mutation sites but also on other domains. In silico analysis revealed that NP_000496.2:p.(Pro182Leu) may be BENIGN, NP_000496.2:p.(Cys559Arg) may be damaging, and that NM_000505.4:c.398-1G>A and NM_000505.4:c.1681-1G>A are crucial for splicing. Conclusion: We found six types of mutations, of which five were novel. The two missense mutation sites might be closely related to the function of coagulation factor XII. The mutations were the primary culprits of factor XII deficiency.