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TCHH gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

TCHH gene

The TCHH gene provides instructions for making the protein trichohyalin, which is essential for the structural integrity and shape of hair shafts.

Normal Function

The TCHH gene provides instructions for making a protein called trichohyalin. This protein is primarily found in hair follicles and the hair shaft. Once produced, trichohyalin is modified to attach to other trichohyalin proteins and molecules called keratin intermediate filaments. These organized cross-links form dense networks that give the hair shaft its cylindrical shape.

Health Conditions Related to Genetic Changes

Uncombable hair syndrome

At least one mutation in the TCHH gene has been found to cause uncombable hair syndrome. This condition is characterized by dry, frizzy, blond scalp hair that cannot be combed flat. The condition typically improves over time, and by adolescence, hair often lies flat and has a normal or nearly normal texture.

The identified mutation leads to a premature stop signal in the instructions for making trichohyalin, resulting in an abnormally short protein with severely reduced activity. This deficiency reduces the cross-links formed between trichohyalin proteins and keratin intermediate filaments. Consequently, the cross-section of the hair shaft becomes triangular, heart-shaped, or flat, resulting in the frizzy hair characteristic of the syndrome.

Other Names for This Gene

  • AHF
  • THH
  • THL
  • TRHY

Frequently Asked Questions

Diagnosis typically begins with a physical examination of the hair shafts, often using a microscope to observe the characteristic triangular or heart-shaped cross-sections of the hair. To confirm the genetic cause, a healthcare provider may order genetic testing to identify specific mutations in the TCHH gene. This testing can be done through a blood or saliva sample and is particularly useful if the clinical presentation is ambiguous or if the family history suggests a genetic component.
Yes, the condition generally improves over time. While the hair is often dry, frizzy, and difficult to comb in infancy and early childhood, it frequently becomes softer and lies flatter as the child enters adolescence. By the teenage years, many individuals have hair that appears normal or nearly normal in texture and manageability, although some may retain slight coarseness or dryness.
Uncombable hair syndrome caused by TCHH gene mutations is typically inherited in an autosomal dominant pattern, meaning only one copy of the altered gene is needed to cause the condition. However, many cases result from new (de novo) mutations that occur in the egg or sperm cell or early in embryonic development, with no prior family history. If a parent has the condition, there is a 50 percent chance of passing the mutation to each child. Genetic counseling is recommended to assess risk for future pregnancies.
No, mutations in the TCHH gene specifically affect the structure of the hair shaft and do not impact internal organ function or overall physical health. The condition is limited to the hair, and individuals with uncombable hair syndrome are otherwise healthy. There are no known complications related to skin, nails, or systemic health associated with this specific genetic change.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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