A novel GRHL2 nonsense variant impairs auditory function via a gain-of-function mechanism in autosomal dominant...

Hearing loss (HL) is genetically and phenotypically heterogeneous. Variants in GRHL2, which encodes the Grainyhead-like 2 transcription factor, cause autosomal dominant nonsyndromic HL (DFNA28). Only six pathogenic GRHL2 variants have been reported, predominantly associated with high-frequency HL.

To elucidate the molecular etiology of ADNSHL presenting with low-to-mid frequency HL in a four-generation Chinese Han family.

Whole exome sequencing was performed to identify the candidate variant, followed by Sanger sequencing for co-segregation analysis. Functional assessments included protein subcellular localization, luciferase assays and co-immunoprecipitation.

A novel nonsense variant, c.648C>G (p.Tyr216Ter), in GRHL2 was identified and co-segregated with the HL phenotype. Contrary to the characteristic high-frequency HL in DFNA28, the 11-year-old proband (IV:4) displayed low-to-mid frequency HL. The variant introduces a premature termination codon, producing a truncated protein missing 409 C-terminal amino acids. Initially classified as likely pathogenic according to the ACMG/AMP guidelines, functional analysis demonstrated cytoplasmic mislocalization and abnormal transcriptional upregulation, potentially via interaction with wild-type GRHL2, prompting reclassification to pathogenic.

Our findings broaden the GRHL2 mutational spectrum, support a gain-of-function mechanism in DFNA28, and establish GRHL2 as a gene associated with low-to-mid frequency HL, expanding known genotype-phenotype correlations.