GJB2 and hereditary palmoplantar keratoderma: Mutations in the GJB2 gene encoding connexin 26 are detrimental to function of cochlea, palmoplantar epidermis, hair follicles, corneal epithelium, and sweat glands and ducts, causing nonsyndromic sensorineural deafness, palmoplantar keratoderma and hearing impairment, Vohwinkel syndrome, and KID syndrome [8–11].