Encyclopedia
Tenascin XB: The TNXB gene provides instructions for making a protein called tenascin-X.
- genes
1. Normal Function
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.
2. Health Conditions Related to Genetic Changes
2.1. Ehlers-Danlos syndrome
Mutations in the TNXB gene cause a very small percentage of all cases of a form of Ehlers-Danlos syndrome called the hypermobile 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 hypermobile 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 hypermobile 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 hypermobility and chronic joint pain. The signs and symptoms of benign joint hypermobility syndrome overlap significantly with those of the hypermobile 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 a form of the disorder that is often called the classical-like type. Its signs and symptoms are similar to the classical type of Ehlers-Danlos syndrome, 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.
3. Other Names for This Gene
- hexabrachion-like
- HXBL
- tenascin XB1
- tenascin XB2
- TENX
- TENX_HUMAN
- TNX
- TNXB1
- TNXB2
- TNXBS
- XB
- XBS
This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/gene/tnxb
References
- Demirdas S, Dulfer E, Robert L, Kempers M, van Beek D, Micha D, van EngelenBG, Hamel B, Schalkwijk J, Loeys B, Maugeri A, Voermans NC. Recognizing thetenascin-X deficient type of Ehlers-Danlos syndrome: a cross-sectional study in17 patients. Clin Genet. 2017 Mar;91(3):411-425. doi: 10.1111/cge.12853.
- Hendriks AG, Voermans NC, Schalkwijk J, Hamel BC, van Rossum MM. Well-defined clinical presentation of Ehlers-Danlos syndrome in patients with tenascin-Xdeficiency: 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 recessiveEhlers-Danlos syndrome. Am J Med Genet A. 2005 May 15;135(1):75-80.
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- Tinkle B, Castori M, Berglund B, Cohen H, Grahame R, Kazkaz H, Levy H.Hypermobile Ehlers-Danlos syndrome (a.k.a. Ehlers-Danlos syndrome Type III andEhlers-Danlos syndrome hypermobility type): Clinical description and naturalhistory. Am J Med Genet C Semin Med Genet. 2017 Mar;175(1):48-69. doi:10.1002/ajmg.c.31538.
- 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 EngelenBG. Ehlers-Danlos syndrome due to tenascin-X deficiency: muscle weakness andcontractures 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 withhypermobility type of Ehlers-Danlos syndrome. Am J Hum Genet. 2003Jul;73(1):214-7.
- Zweers MC, Dean WB, van Kuppevelt TH, Bristow J, Schalkwijk J. Elastic fiberabnormalities in hypermobility type Ehlers-Danlos syndrome patients withtenascin-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. 2004Sep;50(9):2742-9. Review.
