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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed November 2015

What is the official name of the TNXB gene?

The official name of this gene is “tenascin XB.”

TNXB is the gene's official symbol. The TNXB gene is also known by other names, listed below.

What is the normal function of the TNXB gene?

The TNXB gene provides instructions for making a protein called tenascin-X. This protein plays an important role in organizing and maintaining the structure of tissues that support the body's muscles, joints, organs, and skin (connective tissues). In particular, studies suggest that it helps to regulate the production and assembly of certain types of collagen. Collagens are a family of proteins that strengthen and support connective tissues throughout the body. Tenascin-X is also involved in regulating the structure and stability of elastic fibers, which provide flexibility and stretchiness (elasticity) to connective tissues.

Does the TNXB gene share characteristics with other genes?

The TNXB gene belongs to a family of genes called fibronectin type III domain containing (fibronectin type III domain containing).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

How are changes in the TNXB gene related to health conditions?

Ehlers-Danlos syndrome - caused by mutations in the TNXB gene

Mutations in the TNXB gene cause a very small percentage of all cases of a form of Ehlers-Danlos syndrome called the hypermobility type. Ehlers-Danlos syndrome is a group of disorders that affect the connective tissues that support the skin, bones, blood vessels, and many other organs and tissues. The hypermobility type is characterized by an unusually large range of joint movement (hypermobility). The mutations that cause this form of the disorder occur in one copy of the TNXB gene in each cell. These mutations reduce the amount of functional tenascin-X that cells produce, which decreases the ability of tenascin-X to interact with collagens and elastic fibers. These changes weaken connective tissues in many parts of the body, which results in the signs and symptoms of the hypermobility type of Ehlers-Danlos syndrome.

Some people with a condition called benign joint hypermobility syndrome (BJHS) also make a reduced amount of tenascin-X protein, although no TNXB gene mutations have been identified in these individuals. This condition causes an unusually large range of joint movement (hypermobility) and chronic joint pain. The signs and symptoms of benign joint hypermobility syndrome overlap significantly with those of the hypermobility type of Ehlers-Danlos syndrome. Studies suggest that they may be forms of the same condition.

Some people with Ehlers-Danlos syndrome have mutations in two copies of the TNXB gene in each cell. These individuals have signs and symptoms similar to a form of the condition called the classical type, including hypermobility and skin that is soft, highly stretchy (elastic), and fragile. However, affected individuals do not have the unusual scarring that is characteristic of that type. Mutations that occur in both copies of the TNXB gene prevent production of any tenascin-X protein. A loss of this protein severely disrupts the organization of collagen fibrils and elastic fibers, which significantly weakens connective tissues.

Where is the TNXB gene located?

Cytogenetic Location: 6p21.3

Molecular Location on chromosome 6: base pairs 32,041,155 to 32,109,374

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The TNXB gene is located on the short (p) arm of chromosome 6 at position 21.3.

The TNXB gene is located on the short (p) arm of chromosome 6 at position 21.3.

More precisely, the TNXB gene is located from base pair 32,041,155 to base pair 32,109,374 on chromosome 6.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about TNXB?

You and your healthcare professional may find the following resources about TNXB helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the TNXB gene or gene products?

  • hexabrachion-like
  • HXBL
  • tenascin XB1
  • tenascin XB2
  • TENX
  • TNX
  • TNXB1
  • TNXB2
  • XB
  • XBS

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding TNXB?

benign ; cell ; chronic ; collagen ; elastic ; gene ; hypermobility ; joint ; protein ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Hendriks AG, Voermans NC, Schalkwijk J, Hamel BC, van Rossum MM. Well-defined clinical presentation of Ehlers-Danlos syndrome in patients with tenascin-X deficiency: a report of four cases. Clin Dysmorphol. 2012 Jan;21(1):15-8. doi: 10.1097/MCD.0b013e32834c4bb7. (
  • Lindor NM, Bristow J. Tenascin-X deficiency in autosomal recessive Ehlers-Danlos syndrome. Am J Med Genet A. 2005 May 15;135(1):75-80. (
  • NCBI Gene (
  • Petersen JW, Douglas JY. Tenascin-X, collagen, and Ehlers-Danlos syndrome: tenascin-X gene defects can protect against adverse cardiovascular events. Med Hypotheses. 2013 Sep;81(3):443-7. doi: 10.1016/j.mehy.2013.06.005. Epub 2013 Jul 3. (
  • Schalkwijk J, Zweers MC, Steijlen PM, Dean WB, Taylor G, van Vlijmen IM, van Haren B, Miller WL, Bristow J. A recessive form of the Ehlers-Danlos syndrome caused by tenascin-X deficiency. N Engl J Med. 2001 Oct 18;345(16):1167-75. (
  • Valcourt U, Alcaraz LB, Exposito JY, Lethias C, Bartholin L. Tenascin-X: beyond the architectural function. Cell Adh Migr. 2015;9(1-2):154-65. doi: 10.4161/19336918.2014.994893. Review. (
  • Voermans NC, Jenniskens GJ, Hamel BC, Schalkwijk J, Guicheney P, van Engelen BG. Ehlers-Danlos syndrome due to tenascin-X deficiency: muscle weakness and contractures support overlap with collagen VI myopathies. Am J Med Genet A. 2007 Sep 15;143A(18):2215-9. (
  • Zweers MC, Bristow J, Steijlen PM, Dean WB, Hamel BC, Otero M, Kucharekova M, Boezeman JB, Schalkwijk J. Haploinsufficiency of TNXB is associated with hypermobility type of Ehlers-Danlos syndrome. Am J Hum Genet. 2003 Jul;73(1):214-7. (
  • Zweers MC, Dean WB, van Kuppevelt TH, Bristow J, Schalkwijk J. Elastic fiber abnormalities in hypermobility type Ehlers-Danlos syndrome patients with tenascin-X mutations. Clin Genet. 2005 Apr;67(4):330-4. (
  • Zweers MC, Hakim AJ, Grahame R, Schalkwijk J. Joint hypermobility syndromes: the pathophysiologic role of tenascin-X gene defects. Arthritis Rheum. 2004 Sep;50(9):2742-9. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: November 2015
Published: February 1, 2016