TMC6/8-associated epidermodysplasia verruciformis: germline variants and a complex structural alteration in a skin cancer predisposition syndrome

Hereditary epidermodysplasia verruciformis (EV) represents a paradigmatic inherited cutaneous syndrome linking viral susceptibility, immunity, and oncogenesis. Although biallelic variants in CIB1, TMC6, and TMC8-encoding components of the keratinocyte-intrinsic antiviral complex-underlie most cases, the full mutational spectrum and its oncologic implications remain incompletely defined. We performed integrated genomic, histopathological, and longitudinal clinical analyses in six affected individuals from five unrelated families with confirmed hereditary EV. Comprehensive short-read sequencing, copy-number assessment, and optical genome mapping (OGM) were used to delineate the underlying genetic alterations, followed by long-range PCR and Sanger validation. Pathogenic or likely pathogenic germline variants affecting TMC6 or TMC8 were identified in all probands, providing molecular confirmation of disease. Four variants were novel, including splice-site, frameshift, and in-frame deletions. In one proband, OGM revealed a previously unrecognised complex del-inv-del structural variant spanning both TMC6 and TMC8-the first reported example in hereditary EV. This rearrangement, confirmed at base-pair resolution, co-segregated with a synonymous TMC8 variant that served as a practical haplotypic marker for carrier testing. Clinically, all patients developed cutaneous squamous cell carcinoma (SCC), and several exhibited multifocal or aggressive disease, underscoring the deterministic malignant potential of hereditary EV. This study broadens the genetic and phenotypic spectrum of TMC6/TMC8-associated EV, establishes complex structural rearrangement in the molecular etiology, and consolidates hereditary EV as a recessive cancer predisposition syndrome. Integrating high-resolution genome mapping into diagnostic workflows may uncover concealed allelic architecture in unresolved hereditary cancer syndromes.