Rare
genetic causes of hypotrichosis
More than 300 genetic conditions exist that have hair abnormalities as one component. The hypohidroticectodermal dysplasias are a group of rare inheriteddisorders characterized by sparse hair, scanty sweat glands, and poor development of the nails and teeth. (Figs 13.13 and 13.14). Heat stroke may follow inad-equate sweat production. One type is inherited as an X-linked recessive. The responsible gene for this type (on chromosome Xq12) has recently been shown to encode for a protein (ectodysplasin) involved in the regulation of ectodermal appendage formation. The genes responsible for the dominant/recessive types encode for the ectodysplasin receptor.
In
other inherited disorders the hair may be beaded and brittle (monilethrix);
flattened and twisted (pilitorti); kinky (Menkes’
syndrome caused by muta-tions in a gene encoding for a copper
transport-ing membrane protein); like bamboo (Netherton’ssyndrome,
caused by a gene on chromosome 5q32encoding a serine protease inhibitor);
partly broken in many places (trichorrhexis nodosa);
‘woolly’ or ‘uncombable’.
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