Keratin 2A is a type II cytokeratin, also known as Keratin 2E or Keratin 2. It is found largely in the upper spinous layer of epidermal keratinocytes and mutations in the gene encoding this protein have been associated with ichthyosis bullosa of Siemens.Although the expression of KRT9 is limited to palmoplantar epidermis, KRT2 is expressed not only in this tissue but also in other regions, notably the epidermis covering the knee, thigh, and groin. It is not known whether these keratins simply replace their respective type I or type II counterpart in the preexisting KRT1/KRT10 network or dimerize with another, as yet undiscovered keratin partner. The other major epidermal keratins, KRT6 and KRT16, are normally expressed in the outer root sheath of the hair follicle and in palmoplantar epidermis.