A novel mutation in the keratin 4 gene causing white sponge naevus.

White sponge naevus (WSN) is a rare, autosomal dominant disorder that predominantly affects noncornified stratified squamous epithelia, most commonly the buccal mucosa. Clinically, WSN manifests as thickened spongy mucosa with a white opalescent tint in the mouth and may be confused with other disorders that cause white lesions on oral mucosa. Recent studies have identified pathogenic mutations in KRT4 and KRT13, the genes encoding mucosa-specific keratins, in WSN. To search for possible mutations in KRT4 and KRT13. We report a case of WSN in a young man who presented with diffuse irregular whitish plaques involving the buccal and gingival mucosae and the tongue. Results Pathologically, the affected mucosa showed epithelial thickening, parakeratosis and extensive vacuolization of the suprabasal keratinocytes. Mutation analysis revealed a heterozygous missense mutation 1345G-->A in KRT4, predicting an amino acid change, E449K, in the 2B domain of the K4 polypeptide. We report the first mutation analysis of a Taiwanese patient with WSN. Potentially this novel mutation could disrupt the stability of keratin filaments and result in WSN.