When the obtained results are related to information on the expression of connexins in pathologically altered epithelia of the mammalian oral cavity (i.e., oral squamous cell carcinoma and tongue papilloma) and epidermis (i.e., psoriasis, viral warts, or palmoplantar keratoderma), an increase in the expression of Cx26 and Cx43 is noted [25,28,46,47,48,49]. This evidence concerns the gene GJA1 and hereditary palmoplantar keratoderma.