Measurement of Serum Tenascin-X in Joint Hypermobility Syndrome Patients.

Joint hypermobility syndrome (JHS) (also termed hypermobility type Ehlers-Danlos syndrome, hEDS) is a heritable connective tissue disorder that is characterized by generalized joint hypermobility, chronic pain, fatigue, and minor skin changes. Initially, it was reported that there is a small subset of patients with JHS/hEDS who have haploinsufficiency of tenascin-X (TNX). However, the relationship between TNXB and JHS/hEDS has not been reported at all afterwards. EDS was reclassified into thirteen types in 2017, and the causative gene of JHS/hEDS remained to be identified. Therefore, in this study in order to determine whether JHS/hEDS can be diagnosed by the concentrations of serum form of TNX (sTNX), we measured the concentrations of sTNX in 17 JHS/hEDS patients. The sTNX concentrations in half of the JHS/hEDS patients were significantly lower than those in healthy individuals. No mutations, insertions or deletions were detected in the TNX exon sequence of the JHS/hEDS patients except for one in patient. That patient has a heterozygous mutation. A correlation between sTNX concentration and mutation of the TNXB genomic sequence was not found in the JHS/hEDS patients. These results indicate that the decrease in sTNX concentration could be used as a risk factor for JHS/hEDS.