A novel SERPING1 splice-site variant (c.1029 + 2T > A) causing hereditary angioedema type I: functional characterization and clinical analysis

Abstract Background Hereditary angioedema (HAE) is a rare autosomal dominant disorder predominantly caused by mutations in the SERPING1 gene, which encodes C1 esterase inhibitor (C1-INH). HAE is characterized by recurrent self-limiting episodes of subcutaneous and submucosal edema that can be life-threatening when the upper airway is involved. Diagnostic delays and misdiagnoses are common due to the clinical overlap with allergic and histamine-mediated angioedema. Identification and functional characterization of novel SERPING1 variants is essential for refining the mutational spectrum of this disease, enhancing molecular diagnostics, and guiding individualized therapeutic strategies. Methods A 31-year-old female with a ten-year history of recurrent angioedema was diagnosed with HAE type I based on reduced serum C4, C1-INH antigen levels, and C1-INH functional activity. Sanger sequencing of the SERPING1 gene was performed to identify the causative variant. Functional characterization of the identified splice-site variant was conducted using reverse transcription-PCR (RT-PCR) on patient-derived peripheral blood RNA and an in vitro minigene splicing assay in HEK293T cells. A retrospective analysis of seven HAE patients was performed, including clinical characterization, laboratory profiling, genetic analysis, and treatment outcomes. Results A novel heterozygous splice-site variant, c. 1029 + 2T > A, was identified at the canonical splice donor site of intron 6 of SERPING1. RT-PCR revealed reduced wild-type transcript expression and an aberrant transcript resulting from complete exon 6 skipping (c. 890₁029del), predicted to cause a frameshift and premature termination codon (p. Ala297Glyfs*25). The minigene assay confirmed that the mutant construct produced no detectable canonical transcript; instead, three aberrant splice isoforms were identified, with exon 6 skipping as the predominant event. Long-term prophylactic treatment with Lanadelumab (300 mg subcutaneously every two weeks) achieved zero breakthrough attacks over a six-month follow-up period. In the retrospective cohort of seven patients, six were classified as type I and one as type II HAE. Seven distinct variants of the SERPING1 gene were identified. Among these patients, five received long-term prophylaxis with Lanadelumab, which resulted in significant reductions in the frequency of attacks. Conclusion We identified and functionally characterized a novel SERPING1 splice-site variant, c. 1029 + 2T > A, which disrupts canonical mRNA splicing, primarily through exon 6 skipping, leading to C1-INH haploinsufficiency and type I HAE. Our retrospective analysis expands the mutational spectrum of SERPING1 and demonstrates the clinical efficacy of Lanadelumab as a long-term prophylactic therapy. These findings underscore the importance of integrating genetic testing and functional validation in the diagnosis and management of HAE.