Tenascin-X (TNX) is an extracellular matrix protein which is encoded by the gene Tenascin XB (TNXB). This gene is located on chromosome 6. Unfortunately, there are not many information about the function of TNX available so far. However, researchers proposed that TNX is supposed to stabilize the room between elastic fibers and collagen fibers.
A couple of publications were able to show a connection between TNX and other diseases.
Most scienticsts described TNXB mutations and their importance only in correlation with TNX deficiency or haploinsufficiency. The fact that TNX deficiency leads to an EDS phenotype was clarified by several publications (see EDS publications), and in March 2017 TNX deficiency was officially included in the new classification as classical-like EDS (clEDS).
One big question remains: What effects do heterozygous TNXB missense mutations have on the protein level?
Only one publication (Zweers et al.) describes how three different TNXB missense mutations affect the patients. Two were described as probably pathogenic and one as not pathogenic.
(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. Clinical genetics. 2005 Apr 1;67(4):330-4.)
TNX deficiency was shown to have myopathic features, neuromuscular symptoms, and could have an overlap with collagen VI-related myopathies, such as Ullrich congenital muscular dystrophy (UCMD).
Additionally, scientists discovered another distinct EDS type called CAH-X. Patients with this EDS type showed signs of EDS and CAH (congenital adrenal hyperplasia). The gene that is disease-causing for CAH overlaps with the TNXB gene.