May serve an important special function either in the mature palmar and plantar skin tissue or in the morphogenetic program of the formation of these tissues. Plays a role in keratin filament assembly. Heterotetramer of two type I and two type II keratins. Expressed in the terminally differentiated epidermis of palms and soles. Induced by intrinsic regulatory mechanisms and by extrinsic signals from a subset of dermal palmoplantar fibroblasts. The disease is caused by variants affecting the gene represented in this entry. There are two types of cytoskeletal and microfibrillar keratin, I (acidic) and II (neutral to basic) (40-55 and 56-70 kDa, respectively). Belongs to the intermediate filament family. Was originally thought to be a 60 kDa chain of placental scatter protein.