Keratin 17 Expression in the Hard Epithelial Context of the Hair and Nail, and Its Relevance for the Pachyonychia Congenita Phenotype

The study investigated the expression of keratin 17 (K17) in hair and nail structures, focusing on its role in pachyonychia congenita (PC), a genetic disorder affecting skin appendages. K17 was found to be expressed in the medulla of the hair shaft and the nail matrix, suggesting its involvement in the development and maintenance of these structures. In humans, K17 expression was noted in eyebrow and facial hair, associated with the pili torti phenotype in type 2 PC, linked to K17 mutations. The study highlighted the coexpression of K17 with keratins 6 and 16 in the nail bed epithelium, suggesting that nail alterations in PC arise from hyperkeratosis of the nail bed. The findings indicated that K17 expression is regulated at the transcriptional level and may be influenced by LEF/TCF transcription factors, contributing to the unique features of PC.