The KRT1 gene provides instructions for making a protein called keratin 1. Keratins are a group of tough, fibrous proteins that form the structural framework of cells called keratinocytes that make up the skin, hair, and nails. Keratin 1 is produced in keratinocytes in the outer layer of the skin (the epidermis), including the skin on the palms of the hands and soles of the feet.
The keratin 1 protein partners with another keratin protein, either keratin 9 or keratin 10, to form molecules called keratin intermediate filaments. These filaments assemble into strong networks that provide strength and resiliency to the skin and protect it from being damaged by friction and other everyday physical stresses.
Dozens of mutations in the KRT1 gene have been found in people with epidermolytic hyperkeratosis. This condition is a skin disorder characterized by red, blistering skin at an early age and thick skin (hyperkeratosis) later in life. People with KRT1 gene mutations typically have PS-type epidermolytic hyperkeratosis, which features thick skin on the palms of the hands and soles of the feet (palmoplantar hyperkeratosis) in addition to other parts of the body.
Most KRT1 gene mutations associated with epidermolytic hyperkeratosis change a single protein building block (amino acid) in the keratin 1 protein. These amino acid changes commonly occur in regions of the protein that play a role in intermediate filament formation. The mutations alter the keratin 1 protein and seem to affect how intermediate filaments interact with each other to form networks. The altered proteins still form intermediate filaments, but the intermediate filament networks are weaker and do not function normally. Without a strong network, skin cells become fragile and are easily damaged, which can lead to blistering in response to friction or mild trauma. It is unclear how these mutations cause the overgrowth of keratinocytes that results in hyperkeratotic skin.
KRT1 gene mutations are involved in many other skin disorders. In several of these conditions, there is palmoplantar hyperkeratosis, but the skin on other parts of the body is usually not affected. A condition called epidermolytic palmoplantar keratoderma caused by KRT1 gene mutations is relatively mild. Affected individuals typically have palmoplantar hyperkeratosis with detachment or loosening of the epidermis (epidermolysis), usually seen as blistering. People with nonepidermolytic palmoplantar keratoderma have palmoplantar hyperkeratosis with no evidence of epidermolysis. In striate palmoplantar keratoderma type 3, the skin thickening on the palms and soles follows a specific pattern.
KRT1 gene mutations are also responsible for a skin disorder called Curth-Macklin ichthyosis hystrix. This condition involves severe hyperkeratosis on the palms and soles and sometimes the skin over large joints or on the torso. This condition is distinguished by specific changes in the keratinocytes.
Another skin condition caused by genetic changes in the KRT1 gene called cyclic ichthyosis with epidermolytic hyperkeratosis is similar to epidermolytic hyperkeratosis, but the skin changes disappear for short periods, then recur. The recurrent skin changes can last for weeks or months.
67 kDa cytokeratin
hair alpha protein
keratin 1, type II
keratin, type II cytoskeletal 1
type-II keratin Kb1