Objective: This study aimed to analyze the phenotype and genotype of a consanguineous marriage pedigree with inherited coagulation factor Ⅻ (FⅫ) deficiency and to elucidate the potential molecular pathogenesis.
Clinical presentation: The proband was a 51-year-old male with persistent symptoms of tinnitus. He was found to have a significantly prolonged activated partial thromboplastin time (APTT) at 117.7s (reference range, 29.1∼43.3s) during routine coagulation screening.
Methods: Direct DNA sequencing was performed in the coding regions and flanking sequences of F12 gene to screen for variants. Thromboelastography and thrombin generation assays were conducted to simulate the dynamic changes in the blood coagulation process in vitro and in vivo. The conservatism and pathogenicity of variants were estimated using multiple bioinformatics tools and PyMOL software.
Results: The proband exhibited significantly prolonged APTT, and severely decreased FⅫ activity and antigen levels, who harbored a c.811_813delAAC (p.Asn271del) homozygous deletion variant in exon 9 and a homozygous 46 T/T variant. The thromboelastography assay demonstrated reduced activity of the intrinsic coagulation cascade, whereas the thrombin generation assay showed a normal ability for thrombin formation in the proband. Conservative analysis revealed that Asn271 was completely conserved among homologous species. Moreover, inframe deletion variant p.Asn271del was declared to be pathogenic and could impair structure and function of FⅫ protein, which was assessed by the bioinformatics and protein modeling analysis.
Conclusion: The c.811_813delAAC deletion variant in exon 9 together with C46 T variant of F12 gene may synergistically contribute to the FⅫ deficiency in this pedigree.
Keywords: Coagulation factor Ⅻ deficiency; bioinformatics; genetic analysis; thrombin generation.