The trichohyalin gene is a member of the "fused"gene family. Trichohyalin is a large structural protein abundant in the inner root sheath (IRS) of anagenic (growing) hair follicles and other sites of hard cornification [, ]. It associates with intermediate filaments and associates in regular arrays with keratin intermediate filaments.In humans, a number of genes specifying structural proteins expressed late during epidermal differentiation have been identified and found to be clustered on chromosome 1q21. Therefore, this region is named the epidermal differentiation complex (EDC). The proteins encoded by the EDC genes can be classified into three groups: the precursor proteins of the CE, the S100 family and the "fused"gene family []. In some classification, the "fused gene"family is classified as a subgroup within the S100 gene family []. The "fused"gene family members contain EF hands and internal tandem repeats. It consists of profilaggrin, trichohyalin, repetin, hornerin, the profilaggrin-related protein and cornulin (encoded by c1orf10). They are associated with keratin intermediate filaments and partially cross-linked to the cell envelope (CE) [].
