Editing Keratin (section)

==Clinical significance==
Abnormal growth of keratin can occur in a variety of conditions including [[keratosis]], [[hyperkeratosis]] and [[keratoderma]].

Mutations in keratin gene expression can lead to, among others:
* [[Alopecia areata]]
* [[Epidermolysis bullosa simplex]]
* [[Ichthyosis bullosa of Siemens]]
* [[Epidermolytic hyperkeratosis]]
* [[Steatocystoma multiplex]]
* [[Keratosis pharyngis]]
* Rhabdoid cell formation in [[large cell lung carcinoma with rhabdoid phenotype]]<ref name="Shiratsuchi_2002">{{cite journal | vauthors = Shiratsuchi H, Saito T, Sakamoto A, Itakura E, Tamiya S, Oshiro Y, Oda Y, Toh S, Komiyama S, Tsuneyoshi M | title = Mutation Analysis of Human Cytokeratin 8 Gene in Malignant Rhabdoid Tumor: A Possible Association with Intracytoplasmic Inclusion Body Formation | journal = Modern Pathology : an Official Journal of the United States and Canadian Academy of Pathology, Inc | volume = 15 | issue = 2 | pages = 146–153 | date = February 2002 | pmid = 11850543 | doi = 10.1038/modpathol.3880506 | doi-access = free }}</ref><ref name="Itakura_2001">{{cite journal | vauthors = Itakura E, Tamiya S, Morita K, Shiratsuchi H, Kinoshita Y, Oshiro Y, Oda Y, Ohta S, Furue M, Tsuneyoshi M | title = Subcellular Distribution of Cytokeratin and Vimentin in Malignant Rhabdoid Tumor: Three-Dimensional Imaging with Confocal Laser Scanning Microscopy and Double Immunofluorescence | journal = Modern Pathology : an Official Journal of the United States and Canadian Academy of Pathology, Inc | volume = 14 | issue = 9 | pages = 854–861 | date = September 2001 | pmid = 11557780 | doi = 10.1038/modpathol.3880401 | doi-access = free }}</ref>

Several diseases, such as [[athlete's foot]] and [[ringworm]], are caused by [[dermatophytes|infectious fungi]] that feed on keratin.<ref>{{cite journal | vauthors = Mercer DK, Stewart CS | title = Keratin hydrolysis by dermatophytes | journal = Medical Mycology | volume = 57 | issue = 1 | pages = 13–22 | date = 1 January 2019 | pmid = 29361043 | doi = 10.1093/mmy/myx160 }}</ref>

Keratin is highly resistant to digestive acids if ingested. [[Cat]]s regularly ingest hair as part of their [[Cat behavior#Grooming|grooming behavior]], leading to the gradual formation of [[hairball]]s that may be expelled orally or excreted. In humans, [[trichophagia]] may lead to [[Rapunzel syndrome]], an extremely rare but potentially fatal intestinal condition.

===Diagnostic use===
Keratin expression is helpful in determining epithelial origin in [[anaplastic]] cancers. Tumors that express keratin include [[carcinoma]]s, [[thymoma]]s, [[sarcoma]]s and [[trophoblastic neoplasm]]s. Furthermore, the precise expression-pattern of keratin subtypes allows prediction of the origin of the primary tumor when assessing [[metastasis|metastases]]. For example, [[hepatocellular carcinoma]]s typically express CK8 and CK18, and [[cholangiocarcinoma]]s express CK7, CK8 and CK18, while metastases of [[colorectal carcinoma]]s express CK20, but not CK7.<ref>{{cite journal | vauthors = Omary MB, Ku NO, Strnad P, Hanada S | title = Toward unraveling the complexity of simple epithelial keratins in human disease | journal = The Journal of Clinical Investigation | volume = 119 | issue = 7 | pages = 1794–1805 | date = 1 July 2009 | pmid = 19587454 | pmc = 2701867 | doi = 10.1172/JCI37762 }}</ref>