The human
keratin family comprises 54 members, 28 type I and 26 type II. Out of the 28
type I keratins, 17 are epithelial and 11 are
hair keratins. Similarly, the 26 type II members comprise 20 epithelial and 6
hair keratins. As, however, 9 out of the 37 epithelial
keratins are specifically expressed in the hair follicle, the total number of hair follicle-specific
keratins (26) almost equals that of those expressed in the various forms of epithelia (28). Up to now, more than half of the latter have been found to be involved in inherited diseases, with mutated type I and type II members being roughly equally causal. In contrast, out of the 26 hair follicle-specific
keratins only 5 have, at present, been associated with inherited hair disorders, while one
keratin merely acts as a risk factor. In addition, all hair follicle-specific
keratins involved in pathologies are
type II keratins. Here we provide a detailed description of the respective
hair diseases which are either due to mutations in
hair keratins (
monilethrix,
ectodermal dysplasia of hair and nail type) or hair follicle-specific epithelial
keratins (two mouse models, RCO3 and Ca(Rin) as well as
pseudofolliculitis barbae).