Background: White sponge naevus (WSN) is a rare autosomal dominant condition which is characterised by benign, white spongy plaques (oral leukokeratoses) affecting non-cornifying, wet mucosa. WSN shares several ultrastructural characteristics (eg, epithelial thickening, acanthosis, keratin filament aggregation) with a number of epithelial disorders caused by mutations in keratin genes and to-date two mutations, one in each of the mucosal specific keratins, K4 and K13, have been identified as the molecular basis of the disorder.
Objectives: To identify the molecular basis of WSN in two families with a history of the disease.
Results: Two novel mutations were identified in helix initiation motif of K13. A T-to-C transition was found in the affected members of one family which is predicted to change leucine115 to proline. In the second family, a similar T-to-C transition was found in codon 108 which is predicted to change methionine to threonine in the protein sequence. These changes were not found in 50 unrelated, unaffected individuals.
Conclusions: The mutations in the helix initiation motif of K13 are the cause of WSN in these families. These cases confirm mutations in the mucosal specific keratins as a significant cause of the disorder.