The Common KRT9 Gene Mutation in a Japanese Patient with Epidermolytic Palmoplantar Keratoderma and Knuckle Pad‐Like Keratoses

To the Editor: Epidermolytic palmoplantar keratoderma (EPPK, OMIM 144200) is an autosomal dominant genodermatosis characterized by typically diffuse keratoderma on the palms and soles with a sharp demarcated erythematous margin and histologically by epidermolytic hyperkeratosis (EHK). The involvement of the dorsal aspects of the hands and feet is rare in this disease, but several cases with these features are reported (1–5). The molecular basis of EPPK was recently shown to result from mutations in the KRT9 gene encoding keratin 9 (K9), a cytoskeletal protein expressed exclusively in suprabasal keratinocytes of palmoplantar epidermis. We herein report a case of EPPK with knuckle pad-like keratoses over the dorsal aspects of the hands and its mutation analysis in KRT9. The patient was a thirteen-year-old Japanese boy who was the offspring of healthy non-consanguineous parents. He also has an older sister who is clinically normal. At birth, no skin abnormalities were noted. The Journal of Dermatology Vol. 32: 500–502, 2005