KNG1 mutations (c.618 T > G and c.1165C > T) cause disruption of the Cys206-Cys218 disulfide bond and truncation of the D5 domain leading to hereditary high molecular weight kininogen deficiency.

Background: High molecular weight kininogen (HMWK), encoded by the kininogen-1 (KNG1) gene, is a multifunctional glycoprotein closely associated with the initiation of blood coagulation, tumor growth, and other pathological processes.

Objective: We conducted a study on the clinical phenotype, genetic mutations, and molecular pathogenesis of a female patient with uterine leiomyosarcoma, who presented with HMWK deficiency and an isolated prolonged activated partial thromboplastin time (APTT).

Methods: Clinical phenotyping was conducted through APTT mixing studies, quantitative assessments of intrinsic coagulation factor activities, antigen levels of HMWK, and thromboelastography. Genetic analysis revealed a novel mutation within the KNG1 gene. Subsequent bioinformatics analysis focused on the evolutionary conservation of regions flanking codons 618 and 1165 of the KNG1 gene, with an aim of predicting the mutation's functional impact.

Results: Clinical phenotypic analysis indicated a severe deficiency of HMWK antigen levels in the patient, with levels below 1.0 % of normal. Genetic sequencing identified two mutation sites in the KNG1 gene: a novel missense mutation in exon 5, c.618 T > G (p.Cys206Trp), which leads to disruption of the disulfide bond between Cys206 and Cys218, and a known nonsense mutation in exon 10, c.1165C > T (p.Arg389X), resulting in truncation of the D5 domain in the HMWK protein and reducing its quantity. These two mutations collectively impact the activation of HMWK within the coagulation system.

Conclusion: The compound heterozygous mutations, c.618 T > G (p.Cys206Trp) and c.1165C > T (p.Arg389X), result in a loss of HMWK function, leading to a deficiency in the kinin system and consequently a significant prolongation of the APTT. These findings advance understanding of coagulation factor deficiencies and inform diagnostic and therapeutic approaches for HMWK deficiency, potentially enhancing clinical management strategies.