TNXB Gene

The TNXB gene (TNXB stands for "Tenascin XB") is a protein-coding gene located on chromosome 6p21.33-p21.32. The duplicated copy of this gene is incomplete and represents a pseudogene that is transcribed but does not code for a protein. The structure of this gene is unusual in that it overlaps at its 5' and 3' ends with the CREBL1 and CYP21A2 genes. Several transcript variants encoding different isoforms have been found for the TNXB gene.

The TNXB gene encodes a member of the tenascin family of extracellular matrix glycoproteins. Tenascins have an anti-adhesive effect, in contrast to fibronectin, which is adhesive. This protein is thought to play a role in matrix maturation during wound healing. It accelerates the formation of collagen fibrils. The TNCB gene product may play a role in supporting the growth of epithelial tumors.

Its deficiency is associated with Ehlers-Danlos syndrome. The TNXB gene is located in the major histocompatibility complex (MHC) class III region on chromosome 6. It is one of four genes in this cluster that have been duplicated.

Diseases associated with TNXB include:

• the"classical-like" Ehlers-Danlos syndrome

and

• Vesicoureteral Reflux 8 (OMIM: 615963/ Gbadegesin RA et al. 2013).

1. Burch GH et al (1997) Tenascin-X deficiency is associated with Ehlers-Danlos syndrome. Nature Genet 17: 104-108.
2. Chen W et al (2009) The phenotypic spectrum of contiguous deletion of CYP21A2 and tenascin XB: quadricuspid aortic valve and other midline defects. Am J Med Genet 149A: 2803-2808.
3. Gbadegesin RA et al (2013) TNXB mutations can cause vesicoureteral reflux. J Am. Soc. Nephrol. 24: 1313-1322.
4. Kirschner J et al (2005) Ullrich congenital muscular dystrophy: connective tissue abnormalities in the skin support overlap with Ehlers-Danlos syndromes. Am J Med Genet 132A: 296-301.
5. Larsson LG et al (1987) Hypermobility: features and differential incidence between the sexes. Arthritis Rheum. 30: 1426-1430.
6. Lindor NM et al.(2005) Tenascin-X deficiency in autosomal recessive Ehlers-Danlos syndrome. Am. J Med Genet 135A: 75-80.
7. Micale L et al. (2019) Novel TNXB Variants in Two Italian Patients with Classical-Like Ehlers-Danlos Syndrome. Genes (Basel) 10: doi: 10.3390/genes10120967.
8. Voermans NC et al. (2014) Compound heterozygous mutations of the TNXB gene cause primary myopathy. (Letter) Neuromusc Disord 24: 88-89.