The KRT4 gene provides instructions for making a protein called keratin 4. Keratins are a group of tough, fibrous proteins that form the structural framework of epithelial cells, which are cells that line the surfaces and cavities of the body. Keratin 4 is found in the moist lining (mucosae) of the mouth, nose, esophagus, genitals, and anus.
Keratin 4 partners with a similar protein, keratin 13 (produced from the KRT13 gene), to form molecules known as intermediate filaments. These filaments assemble into strong networks that provide strength and resilience to the different mucosae. Networks of intermediate filaments protect the mucosae from being damaged by friction or other everyday physical stresses.
At least six mutations in the KRT4 gene have been found to cause white sponge nevus, a condition that results in the formation of white patches of tissue called nevi (singular: nevus) that appear as thickened, velvety, sponge-like tissue. These nevi most often occur on the mouth (oral) mucosa (plural: mucosae). Rarely, white sponge nevus occurs on the mucosae of the nose, esophagus, genitals, or anus.
The KRT4 gene mutations that cause white sponge nevus disrupt the structure of keratin 4. As a result, keratin 4 does not fit together properly with keratin 13, leading to the formation of irregular intermediate filaments that are easily damaged with little friction or trauma. Fragile intermediate filaments in the oral mucosa might be damaged when eating or brushing one's teeth. Damage to intermediate filaments leads to inflammation and promotes the abnormal growth and division (proliferation) of epithelial cells, causing the mucosae to thicken and resulting in white sponge nevus.
- cytokeratin 4
- keratin 4, type II
- keratin, type II cytoskeletal 4
- type-II keratin Kb4