CK1 (also designed Cytokeratin 1 or KRT1) with 644-amino acid protein (about 70 kDa), is a member of the keratin family. Cytokeratins play a critical role in differentiation and tissue specialization, and they function to maintain the overall structural integrity of epithelial cells. CK1 consist of basic or neutral proteins which are arranged in pairs of heterotypic keratin chains co-expressed during differentiation of simple and stratified epithelial tissues. CK1 is specifically expressed in the spinous and granular layers of the epidermis with family member KRT10 and mutations in these genes have been associated with bullous congenital cthyosiform erythroderma.