TCHH gene

The TCHH gene (TCHH stands for: Trichohyalin) is a protein-coding gene located on chromosome 1q21.3. The gene codes for trichohyalin, an intermediate filament-associated protein that associates in regular arrangements with keratin intermediate filaments (KIF ) of the inner root sheath cells of the hair follicle and the granular layer of the epidermis. It is later cross-linked by isodipeptide bonds.

The TCHH gene belongs to the epidermal differentiation complex, a gene complex comprising over fifty genes that code for proteins involved in the terminal differentiation and keratinization of keratinocytes. In humans, the complex is located on a 1.9 Mbp section of chromosome 1q21.

The protein encoded by this gene forms cross-linked complexes with itself and keratin intermediate filaments to provide mechanical strength to the inner root sheath of the hair follicle. The encoded protein is also important for the structural integrity of the filiform papillae of the tongue. Trichohyalin, together with involucrin, may serve as a scaffolding protein in the organization of the cell envelope or even anchor the cell envelope to the keratin intermediate filaments/KIF network. It may be involved in its own calcium-dependent post-synthetic processing during terminal differentiation.

Diseases associated with TCHH include:

• Uncombable Hair Syndrome 3 (OMIM: 617252)
• and
• Uncombable Hair Syndrome 1 (OMIM: 191480) .

Related pathways include keratinization and nervous system development.

1. Basmanav FB et al. (2016) Mutations in Three Genes Encoding Proteins Involved in Hair Shaft Formation Cause Uncombable Hair Syndrome. Am J Hum Genet 99:1292-1304.
2. Braun-Falco O et al. (1982) On the syndrome: Uncombable hair. Dermatologist 3: 366-372
3. Dupré A, Rochiccioli P, Bonafé JL (1973) "Cheveux incoiffables": anomalie congenitale des cheveux. Bull Soc Franc Dermatol Syph 80: 111-112
4. Dupre A, Bonafe JL (1978) A new type of pilar dysplasia. The uncompable hair syndrome with pili trianguli et canaliculi. Arch Dermatol Res 261: 217-218
5. Hicks J, Metry DW, Barrish J, Levy M (2001) Uncombable hair (cheveux incoiffables, pili trianguli et canaliculi) syndrome: brief review and role of scanning electron microscopy in diagnosis. Ultrastruct Pathol 25: 99-103
6. Ludwig E (1987) Pili canaliculi, a type of unkempt hair. Dermatologist 38: 727-732