Novel variant c.428T>C in FZD4 gene in a pedigree affected by familial exudative vitreoretinopathy: clinical, functional, and structural characterization

INTRODUCTION: Pathogenic variants in FZD4 have been implicated in the pathogenesis of familial exudative vitreoretinopathy (FEVR). We present a family with a novel FZD4 variant and provide functional evidence supporting its pathogenic relevance. MATERIALS AND METHODS: This family-based study included three affected individuals who underwent comprehensive ophthalmic examinations, including best-corrected visual acuity, slit-lamp biomicroscopy, fundus examination, optical coherence tomography, and wide-field retinal imaging. Genetic testing was performed using whole-exome sequencing, followed by Sanger sequencing for variant confirmation and segregation analysis. Functional studies included in vitro cellular expression assays comparing wild-type and mutant FZD4 protein levels, Western blotting analysis, and proteasome inhibition experiments. Protein structural modeling was conducted to assess the impact of the missense variant on FZD4 domain integrity. RESULTS: Proband and three family members underwent comprehensive clinical evaluation. The proband presented with nystagmus, amblyopia, and acute angle-closure glaucoma in the left eye. Intraocular pressure normalized 1 month after lens extraction with intraocular lens implantation and goniosynechialysis. The proband's clinically asymptomatic sister and mother demonstrated peripheral retinal nonperfusion on imaging, consistent with subclinical manifestations of familial exudative vitreoretinopathy. The heterozygous FZD4 c.428T > C (p.Leu143Pro) variant segregated with FEVR-related phenotypes within the family, showing variable expressivity. The variant was classified as a likely pathogenic allele under ACMG/AMP criteria based on its location in the conserved cysteine-rich domain, absent from population databases, consistent with the in silico predictions, phenotype specificity, and functional evidence. Western blotting demonstrated a reduction of mutant FZD4 protein levels when compared with wild-type protein, also partially rescued by the proteasome inhibitor MG132. Structural modeling suggests that p.Leu143Pro substitution disrupts a conserved α-helical region, potentially affecting Wnt ligand binding. CONCLUSIONS: This family-based study identifies a novel FZD4 missense variant associated with FEVR and provides integrated clinical, genetic, functional, and structural evidence, supporting its likely pathogenic relevance. Surgical management of secondary complications, such as angle-closure glaucoma, might stabilize visual outcomes in patients with FZD4-associated FEVR.