Definition: Rare autosomal dominant disorder of the hair shaft. The clinical features of the disease include HYPOTRICHOSIS, dry, and/or brittle hair, with varying degrees of ALOPECIA. Mutations in the hair-specific keratin genes KRTHB1, KRTHB3, or KRTHB6 are associated with monilethrix. Autosomal recessive monilethrix with limited HYPOTRICHOSIS are also known. Mutations in Dsg4, Liph, and P2ry5 protein genes are associated with the recessive form of monilethrix.