Abstract
Background and Clinical Significance: FLNC encodes filamin C, a muscle-scaffolding protein crucial for cardiac integrity. Pathogenic FLNC variants cause diverse cardiomyopathies (hypertrophic, dilated, restrictive, and arrhythmogenic) and myofibrillar myopathies, but their role in congenital cardiac malformations is unclear. Notably, FLNC has not been implicated in structural defects such as Tetralogy of Fallot (TOF) to date. Case Presentation: Two fetuses from the same family were prenatally diagnosed with TOF via ultrasound. The trio whole-exome sequencing of the second fetus and her parents identified a novel heterozygous truncating FLNC variant (NM_001458.5:c.1453C>T, p.Q485*). Sanger sequencing confirmed the same variant in the earlier TOF fetus. The mother carried the variant but was asymptomatic. In vitro mutagenesis in rat cardiomyocytes showed that the mutant FLNC construct produced markedly reduced FLNC proteins compared to the wild type and did not form abnormal cytoplasmic aggregates. Conclusions: We report on a novel FLNC truncating variant associated with fetal TOF, extending the spectrum of FLNC-related cardiac anomalies. The variable outcomes among variant carriers-from fetal TOF to adult cardiomyopathy or no clinical manifestations-underscore the complex genotype-phenotype correlations of filaminopathy. This case highlights the importance of comprehensive genetic evaluation in families with diverse cardiac phenotypes and suggests that additional genetic factors likely influence phenotypic expression.