FSCN2 encodes retinal fascin, a photoreceptor-specific actin-bundling protein that cross-links F-actin into highly ordered bundles 1. The protein is essential for photoreceptor disk morphogenesis and maintaining the structural integrity of photoreceptor outer segments 1. FSCN2 is also localized in stereocilia of hair cells, where it maintains auditory function 2. Mutations in FSCN2 cause autosomal dominant retinitis pigmentosa (ADRP), with the 208delG mutation identified in 3.3% of Japanese ADRP patients 3. The same mutation produces phenotypic variability, also causing autosomal dominant macular degeneration in some families 4. A novel missense mutation (p.Pro406Leu) has been associated with cone dystrophy featuring central ellipsoid zone loss 5. Mouse models with FSCN2 mutations demonstrate progressive photoreceptor degeneration with structural abnormalities of outer segment disks and depressed electroretinogram responses, suggesting haploinsufficiency mechanisms 6. Beyond vision, null mutations in Fscn2 cause progressive hearing loss in mice through hair cell degeneration and stereocilia loss 2. Large-scale sequencing studies identified rare FSCN2 coding variants associated with adult hearing loss 7, establishing the gene's role in both visual and auditory systems.