TNXB

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.

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.