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


Reviewed May 2006

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 is found in the space between cells (the extracellular matrix), where it appears to be important for organizing and maintaining the normal structure of tissue that supports the body's muscles, joints, organs, and skin (connective tissue). Specifically, researchers believe that tenascin-X helps determine how collagen fibrils are deposited in the extracellular matrix. This protein may also regulate the structure and stability of elastic fibers. Collagen fibrils and elastic fibers provide support, strength, and flexibility to connective tissue throughout the body.

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

A small percentage of people with the hypermobility type of Ehlers-Danlos syndrome have mutations in the TNXB gene. These mutations prevent one copy of the TNXB gene from making any functional protein, reducing the total levels of tenascin-X in the body. Researchers believe that reduced levels of tenascin-X disturb the way that collagen is deposited and disrupt the network of elastic fibers in joint ligaments and tendons. Researchers have also discovered that not everyone with a mutation in one copy of TNXB has signs of Ehlers-Danlos syndrome.

Some people with a condition called benign joint hypermobility syndrome (BJHS) also make a reduced amount of tenascin-X protein. 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 the features of the hypermobility type of Ehlers-Danlos syndrome. Recent 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 the classic type, but without the unusual scarring of the classic type. TNXB mutations prevent production of the tenascin-X protein, which disrupts the normal organization of collagen fibrils and elastic fibers. These changes in the structure of connective tissue likely cause the characteristic features of classic Ehlers-Danlos syndrome.

Where is the TNXB gene located?

Cytogenetic Location: 6p21.3

Molecular Location on chromosome 6: base pairs 32,041,154 to 32,109,373

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 32,041,154 to base pair 32,109,373 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 ; connective tissue ; elastic ; extracellular ; extracellular matrix ; gene ; hypermobility ; joint ; mutation ; protein ; syndrome ; tissue

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. (
  • 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: May 2006
Published: September 28, 2015