A spectrum of mutations in keratins K6a, K16 and K17 causing pachyonychia congenita

Background: Pachyonychia congenita (PC) is a rare autosomal dominant keratin disorder, subdivided into two major variants, PC-1 and PC-2. Predominant characteristics include hypertrophic nail dystrophy, focal palmoplantar keratoderma and oral leukokeratosis. Multiple steatocystomas that develop during puberty are a useful feature distinguishing PC-2 from PC-1. At the molecular level it has been shown that mutations in keratin K6a or K16 cause PC-1 whereas those in K6b or K17 lead to PC-2. Objective: To identify mutations in 22 families presenting with clinical symptoms of either PC-1/focal non-epidermolytic palmoplantar keratoderma (FNEPPK) or PC-2. Methods: Mutation analysis was performed on genomic DNA from PC patients by direct sequencing. Results: Here, we report four new missense and five known mutations in K6a; one new deletion and three previously identified missense mutations in K16; plus one known mutation in K17. Conclusion: With one exception, all these heterozygous mutations are within the highly conserved helix boundary motif regions at either end of the keratin rod domain. In one sporadic case, a unique mutation in K16 resulting in deletion of 24 bp was found within the central rod domain, in a child with a phenotype predominantly consisting of focal plantar keratoderma. The identification of mutations in cases of PC is prerequisite for future development of gene-specific and/or mutation-specific therapies. © 2007 Japanese Society for Investigative Dermatology.