[Analysis of a Chinese pedigree affected with hereditary factor Ⅶ deficiency due to compound heterozygous variants of...

To investigate the molecular pathogenic mechanisms of a family with hereditary factor Ⅶ (FⅦ) deficiency.

A family (3 generations, 12 members) with hereditary FⅦ deficiency, in which the proband presented with menorrhagia and was admitted to the First Affiliated Hospital of Wenzhou Medical University in April 2023, was selected as the study subject. Clinical data of the family members were collected. Peripheral venous blood samples were collected from all 12 members for routine coagulation tests and genomic DNA extraction. All exons and flanking sequences of the F7 gene were amplified by PCR and analyzed by Sanger sequencing. Thrombin generation assay was performed to evaluate the coagulation potential of the proband and her parents. Multiple online bioinformatics software tools were used to analyze the conservation and pathogenicity of candidate variants identified in the proband. The pathogenicity of variant was classified according to the Standards and Guidelines for the Interpretation of Sequence Variants released by American College of Medical Genetics and Genomics (ACMG) (hereinafter referred to as ACMG guidelines). Homology modeling of the variant FⅦ protein was performed using homology modeling (SWISS-MODEL). Amino acid sequence alignment between wild-type and variant FⅦ proteins was conducted using MEGA v7, and spatial conformational differences were analyzed using PyMOL to assess the potential impact of the F7 gene variants on the structure and function of the FⅦ protein. This study was approved by the Ethics Committee of the First Affiliated Hospital of Wenzhou Medical University (Ethics No.: KY2022-R193).

Coagulation tests showed that the proband's prothrombin time (PT) was significantly prolonged to 33.1 s, and both factor Ⅶ activity (FⅦ:C) and antigen (FⅦ:Ag) levels were reduced to 2%. Her parents, eldest sister, second sister, younger brother, and four children all showed mildly prolonged PT, with FⅦ:C and FⅦ:Ag levels approximately 50% of normal. Genetic sequencing identified compound heterozygous variants in the F7 gene of the proband: a heterozygous missense variant c.722C>A (p.Thr241Asn) in exon 7, and a heterozygous deletion variant c.1261_1261delA (p.Ile421Ser*fs75) in exon 8. Retrieval from domestic and international databases found no previous reports of the latter variant, suggesting it is novel. Familial co-segregation analysis confirmed that these variants were inherited from her father and mother, respectively. The thrombin generation assay demonstrated that the proband had a significantly decreased peak thrombin height (peak ratio: 29.5%), significantly increased thrombin lag time ratio and time-to-peak ratio (3.03 and 2.93, respectively), but only a mildly decreased endogenous thrombin potential (ETP) ratio of 90.7%. Online bioinformatics analysis indicated that threonine-241 (p.Thr241) in the FⅦ protein was not conserved, while isoleucine-421 (p.Ile421) was highly conserved. Both the p.Thr241Asn and p.Ile421Serfs*75 variant sites in the proband's F7 gene were predicted to be pathogenic. According to the ACMG guidelines, the p.Thr241Asn (PM3+PP1+PP3+PP4+PP5) and p.Ile421Ser*fs75 (PM2+PM4 +PP1+PP3+PP4) variants were both classified as "likely pathogenic". Structural analysis of the FⅦ protein indicated that the p.Ile421Ser*fs75 frameshift variant led to the substitution of Cysteine-428 by Alanine, preventing the formation of a critical disulfide bond between amino acid residues 400 and 428 present in the wild-type FVII protein.

The compound heterozygous variants p.Thr241Asn and p.Ile421Ser*fs75 in the F7 gene are likely the genetic etiology responsible for the reduced FⅦ levels in this hereditary FⅦ deficiency family.