A de Novo Mutation in the Keratin 9 Gene in a Family with Epidermolytic Palmoplantar Keratoderma from Northern Sweden

Sir,Palmoplantar keratodermas (PPKs) constitute a hetero-geneous group of skin disorders with the distinctivetrait of hyperkeratosis of palmoplantar skin. Thedisorders are classified clinically by the morphologyand distribution of the hyperkeratosis, the presence ofassociated cutaneous and non-cutaneous features andby the mode of transmission (1, 2).Familial diffuse epidermolytic PPK (EPPK) is themost studied keratoderma and is characterized bygranular and vacuolar degeneration of the cells of thespinous and granular layer. All mutations reported todate, with one exception, are locatedinthekeratin9gene(KRT9)onchromosome17(1,3). The majority of KRT9mutations reported are missense mutations in exon 1of the KRT9 gene, but there are reports of a stopcodon mutation in exon 1 (4) and of a 3 base pairinsertion in exon 6 (5). The position most frequentlyreported to be mutated in KRT9 is the arginine codonat position 162 in exon 1. In addition to KRT9 mutations,there is a recent study revealing a splice site mutationin the KRT1 gene as the cause of mild EPPK (6).The KRT9 gene appears to be the only keratin genewhose expression is restricted to palmoplantar epider-mis (7, 8). Consequently, individuals that carry amutation in the keratin 9 gene only display the effect ofthe mutation in the palmoplantar skin.Here we report the first observation of a Swedishfamily with EPPK and the attribution of the disorder toa de novo mutation in KRT9.MATERIALS AND METHODS