Clinical and functional characterization of a novel heterozygous mutation c.473T > A (p.Leu158Gln) in the SERPINC1 gene causing recurrent arteriovenous thrombophilia.

BACKGROUND: Hereditary antithrombin deficiency (HATD) is a rare disease caused by mutations in the SERPINC1 gene characterized with venous thromboembolism and/or arterial thrombotic events. We identified a proband with recurrent arterial and venous thrombosis at multiple anatomical sites and subsequently performed comprehensive thrombophilia screening and genetic analysis within the kindred. METHODS: Mutation screening of the SERPINC1 gene in the proband and family members was conducted using Sanger sequencing. Wild-type and mutant (c.473T > A; p.Leu158Gln) SERPINC1 expression plasmids were constructed and transiently transfected into HEK293T cells. Functional consequences of the variant were assessed through immunoblotting, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), and computational structural analysis. RESULTS: Thrombophilia evaluation revealed significantly reduced antithrombin activity (46.2%) in the proband. Sanger sequencing identified an unreported heterozygous missense variant (c.473T > A; p.Leu158Gln) in SERPINC1. Cellular studies demonstrated that this mutation reduced both the quantity and functional activity of secreted antithrombin. Immunoblot analysis indicated a slightly faster migration of the mutant protein compared to wild-type, while immunofluorescence revealed abnormal cytoplasmic aggregation. Bioinformatics analysis confirmed substitution of leucine-158 by glutamine without disruption of conserved disulfide bonds (Cys40-Cys160, Cys128-Cys182, Cys247-Cys430) or N-glycosylation sites (Asn128, Asn167, Asn187, Asn224). CONCLUSION: We establish the c.473T > A (p.Leu158Gln) variant in SERPINC1 as a pathogenic mutation underlying type I HATD, characterized by impaired secretion, cytoplasmic retention, and reduced functional activity of the mutant protein.