Among the cytoplasmic intermediate filaments (IF) proteins, keratins make up the largest family and are expressed specifically in epithelial cells in a cell-specific manner. Keratins include more than 20 unique gene products (termed K1-K20) that are divided into type I (K9-K20) and type II (K1-K8). Most of the type I cytokeratins consist of acidic proteins which are arranged in pairs of heterotypic keratin chains and are clustered in a region of chromosome 17q12-q21. Keratin 16 is a type-I keratin which associates with KRT6 isomers. Mutations in this gene are associated with type 1 pachyonychia congenita, non-epidermolytic palmoplantar keratoderma and unilateral palmoplantar verrucous nevus. It maps to 17q12-q21 region of human chromosome. It is expressed in the hair follicle, nail bed and in mucosal stratified squamous epithelia and, suprabasally, in oral epithelium and palmoplantar epidermis and also found in luminal cells of sweat and mammary gland ducts. Defects in KRT16 are a cause of pachyonychia congenita type 1, nonepidermolytic palmoplantar keratoderma and unilateral palmoplantar verrucous nevus.