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The tenascin-X (TNX) deficient type Ehlers-Danlos syndrome (EDS) is similar to the classical type of EDS. Because of the limited awareness among geneticists and the challenge of the molecular analysis of the TNXB gene, the TNX-deficient type EDS is probably to be under diagnosed. We therefore performed an observational, cross-sectional study. History and physical examination were performed. Results of serum TNX measurements were collected and mutation analysis was performed by a combination of next-generation sequencing (NGS), Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA). Included were 17 patients of 11 families with autosomal recessive inheritance and childhood onset. All patients had hyperextensible skin without atrophic scarring. Hypermobility of the joints was observed in 16 of 17 patients. Deformities of the hands and feet were observed frequently. TNX serum level was tested and absent in 11 patients (seven families). Genetic testing was performed in all families; 12 different mutations were detected, most of which are suspected to lead to non-sense mRNA mediated decay. In short, patients with the TNX-deficient type EDS typically have generalized joint hypermobility, skin hyperextensibility and easy bruising. In contrast to the classical type, the inheritance pattern is autosomal recessive and atrophic scarring is absent. Molecular analysis of TNXB in a diagnostic setting is challenging., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The Ehlers-Danlos syndrome (EDS) is a clinically and genetically heterogeneous group of inherited connective tissue disorders. The six major, well-defined, subtypes are classified according to diagnostic criteria, formalized in the Villefranche revised nosology. Shortly after the publication of these criteria in 1998, a further distinct type of EDS, the tenascin-X (TNX)-deficient type EDS, was reported. The phenotype of this largely unknown type of EDS resembles the phenotype of the classical type of EDS, but its inheritance is autosomal recessive and wound healing is normal; hence, no atrophic scars are present. The clinical diagnosis can be confirmed by the absence of TNX in the serum and by mutation analysis of the TNXB gene. Because the TNX-deficient type EDS is rare and not included in the current diagnostic criteria, this diagnosis is often delayed or even overlooked. Here, we describe four cases which improve the clinical recognition of this type of EDS.

Tenascin-X is a large extracellular matrix glycoprotein that is widely distributed within connective tissues and is associated with an autosomal recessive type of Ehlers-Danlos syndrome (EDS). Tenascin-X represents the first EDS susceptibility gene that does not code for a fibrillar collagen or collagen-processing enzyme. We describe a paediatric case of tenascin-X deficiency and review the literature., (© 2010 The Authors. BJD © 2010 British Association of Dermatologists.)

Objective: Ehlers-Danlos syndrome (EDS) is a clinically and genetically heterogeneous group of heritable connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. Muscle involvement is plausible based on recently discovered interactions between muscle cells and extracellular matrix molecules; however, muscle symptoms are only sporadically reported. We designed a cross-sectional study to find out whether neuromuscular features are part of EDS., Methods: Standardized questionnaires, physical examination, nerve conduction studies, electromyography, muscle ultrasound, and muscle biopsy were performed in 40 EDS patients with the vascular, classic, tenascin-X (TNX)-deficient type EDS, and hypermobility type of EDS caused by TNXB haploinsufficiency., Results: Muscle weakness, myalgia, and easy fatigability were reported by the majority of patients. Mild-to-moderate muscle weakness (85%) and reduction of vibration sense (60%) were common. Nerve conduction studies demonstrated axonal polyneuropathy in five patients (13%). Needle electromyography myopathic features in nine patients (26%) and a mixed neurogenic-myopathic pattern in most (60%). Muscle ultrasound showed increased echo-intensity (48%) and atrophy (50%). Mild myopathic features were seen on muscle biopsy of five patients (28%). Overall, patients with the hypermobility type EDS caused by TNXB haploinsufficiency were least affected., Interpretation: Mild-to-moderate neuromuscular involvement is common in various types of EDS, with a remarkable relation between residual TNX level and degree of neuromuscular involvement, compatible with a dose-effect relation. The findings of this study should increase awareness of neuromuscular symptoms in EDS patients and improve clinical care. They also point to a role of the extracellular matrix in muscle and peripheral nerve function.

Tenascin-X (TNX) is a large, multi-domain, extracellular matrix glycoprotein. Complete deficiency of TNX in humans leads to a recessive form of Ehlers-Danlos syndrome (EDS), and TNX haploinsufficiency is a cause of hypermobility type EDS. EDS patients appear to have a higher risk of several complications during pregnancy, such as pelvic instability, premature rupture of membranes, and postpartum hemorrhage. Here, we present a study of genitourinary and obstetric complications in TNX-deficient women of reproductive age. We have found complications, such as uterus prolapses, that are in agreement with previous findings in other EDS types. In TNX knockout (KO) mice, we have observed mild pregnancy-related abnormalities. Morphological and immunohistological analysis of uterine tissues has not revealed obvious quantitative or spatial differences between TNX KO and wildtype mice with respect to collagen types I, III, V, and XII or elastic fibers. We conclude that TNX-deficient women are at risk of obstetric complications, but that TNX KO mice show only a mild phenotype. Furthermore, we show that TNX is involved in the stability of elastic fibers rather than in their initial deposition.

Tenascin-X (TNX) is a large 450 kDa extracellular matrix protein expressed in a variety of tissues including skin, joints and blood vessels. Deficiency of TNX causes a recessive form of Ehlers-Danlos syndrome characterized by joint hypermobility, skin fragility and hyperextensible skin. Skin of TNX deficient patients shows abnormal elastic fibers and reduced collagen deposition. The mechanism by which TNX deficiency leads to connective tissue alterations is unknown. Here we report that C-terminal domains of human TNX bind to major dermal fibrillar collagens and tropoelastin. We have mapped these interactions to the fibronectin type III repeat 29 (FNIII29) and the C-terminal fibrinogen domain (FbgX) of TNX. In addition we found that FNIII29 of TNX accelerates collagen fibrillogenesis in vitro. We hypothesize that TNX contributes to matrix stability and is possibly involved in collagen fibril formation.

Tenascin-X is an extracellular matrix protein initially identified because the gene encoding it overlaps with the human CYP21B gene. Because studies of gene and protein function of other tenascins had been poorly predictive of essential functions in vivo, we used a genetic approach that critically relied on an understanding of the genomic locus to uncover an association between inactivating tenascin-X mutations and novel recessive and dominant forms of Ehlers-Danlos syndrome (EDS). Tenascin-X provides the first example of a gene outside of the fibrillar collagens and their processing enzymes that causes EDS. Tenascin-X null mice recapitulate the skin findings of the human disease, confirming a causative role for this gene in EDS. Further evaluation of these mice showed that tenascin-X is an important regulator of collagen deposition in vivo, suggesting a novel mechanism of disease in this form of EDS. Further studies suggest that tenascin-X may do this through both direct and indirect interactions with the collagen fibril. Recent studies show that TNX effects on matrix extend beyond the collagen to the elastogenic pathway and matrix remodeling enzymes. Tenascin-X serves as a compelling example of how human "experiments of nature" can guide us to an understanding of genes whose function may not be evident from their sequence or in vitro studies of their encoded proteins., (2005 Wiley-Liss, Inc.)

Ehlers-Danlos syndrome (EDS) is a heterogeneous group of connective tissue disorders with characteristic skin and joint involvement. The concept that EDS is a disease of fibrillar collagen was challenged by the identification of a clinically distinct, recessive type of EDS caused by deficiency of the extracellular matrix protein tenascin-X (TNX). Interestingly, haploinsufficiency of TNX is associated with the dominantly inherited hypermobility type of EDS. In this study, we examined whether missense mutations in the TNX gene can account for some of the cases of hypermobility type EDS. Furthermore, we studied whether missense mutations or heterozygosity for truncating mutations in the TNX gene lead to alterations in the dermal connective tissue. Sequence analysis revealed three missense mutations in TNX in hypermobility type EDS patients, which were not present in 192 control alleles. Morphometric analysis of skin biopsies of these patients showed altered elastic fibers in one of them, suggesting that this missense mutation is disease causing. Light microscopic and ultrastructural changes of the elastic fibers were observed in TNX-haploinsufficient hypermobility type EDS patients, which were not found in hypermobility type EDS patients in whom TNX mutations were excluded. Our results indicate that the observed alterations in elastic fibers are specific for hypermobility type EDS patients with mutations of TNX.

Tenascin-X is a large extracellular matrix protein that is widely expressed in connective tissues during development and in the adult. Genetically determined deficiency of tenascin-X causes the connective tissue disease Ehlers-Danlos syndrome. These patients show reduced collagen density and fragmentation of elastic fibers in their skin. In vitro studies on the role of tenascin-X in elastic fiber biology are hampered because monolayers of fibroblasts do not deposit tenascin-X and elastic fibers into the extracellular matrix. Here, we applied an organotypic culture model of fibroblasts and keratinocytes to address this issue. We investigated the deposition of tenascin-X and elastin into skin-equivalent in vitro and also in vivo after transplantation onto immunodeficient mice. Whereas tenascin-C and fibrillin-1 were readily expressed in the skin-equivalents before transplantation, tenascin-X and elastin were not present. Three weeks post-grafting, a network of elastin was observed that coincided with the appearance of tenascin-X. At the ultrastructural level, microfibrils were observed, some of which were associated with elastin. Transplanted skin-equivalents containing tenascin-X-deficient fibroblasts showed deposition of immunoreactive elastin in similar quantities and distribution as those containing control fibroblasts. This suggests that tenascin-X is important for the stability and maintenance of established elastin fibers, rather than for the initial phase of elastogenesis. Thus, the transplantation of reconstructed skin on nude mice allows the study of tenascin-X and elastin expression and could be used as a model system to study the potential role of tenascin-X in matrix assembly and stability.

Background: We recently described a new autosomal recessive type of Ehlers-Danlos syndrome (EDS) based on a deficiency of the extracellular matrix protein tenascin-X (TNX). TNX-deficient patients have hypermobile joints, hyperextensible skin and show easy bruising. Because of the reported cardiovascular abnormalities in other EDS types and the excessive haematoma formation after mild trauma in TNX-deficient individuals, we investigated whether cardiovascular or coagulation abnormalities occur in these patients., Methods: We examined seven TNX-deficient patients. One of them had a mitral valve prolapse and died postoperatively after valve replacement, before the study was completed., Results: Bleeding time and coagulation factors (INR, APTT, PT and fibrinogen) were all within the normal range. Ultrasonographic examination of the carotid and femoral arteries showed normal vessel wall compliance and distensibility. Echocardiography showed a slight billowing of the mitral valve in two patients from one family. All patients had normal diameters of aortic root and ascending aorta., Conclusion: Although the patient group is small, there are no indications of generalised cardiovascular abnormalities in this type of EDS. We would recommend echocardiography for all these patients at the first evaluation and when a cardiac murmur appears.

Deficiency of the extracellular matrix protein tenascin-X (TNX) was recently described as the molecular basis of a new, recessive type of Ehlers-Danlos syndrome. Here we report gross abnormalities of the elastic fibers and microfibrils in the dermis of these patients, and reduced dermal collagen content, as determined by quantitative image analysis. The ascending, fine elastic fibers in the papillary dermis were absent or inconspicuous and had few branches. The coarse elastic fibers of the reticular dermis were fragmented and clumped. At the ultrastructural level, irregular and immature elastin fibers and fibers devoid of microfibrils were observed. In TNX-deficient patients the dermal collagen density was reduced, but no structural abnormalities in the collagen fibrils were found. These findings suggest that both elastic fiber abnormalities and reduced collagen content contribute to the observed phenotype in TNX-deficient patients.

Background: The Ehlers-Danlos syndrome is a heritable connective-tissue disorder caused by defects in fibrillar-collagen metabolism. Mutations in the type V collagen genes account for up to 50 percent of cases of classic Ehlers-Danlos syndrome, but many other cases are unexplained. We investigated whether the deficiency of the tenascins, extracellular-matrix proteins that are highly expressed in connective tissues, was associated with the Ehlers-Danlos syndrome., Methods: We screened serum samples from 151 patients with the classic, hypermobility, or vascular types of the Ehlers-Danlos syndrome; 75 patients with psoriasis; 93 patients with rheumatoid arthritis; and 21 healthy persons for the presence of tenascin-X and tenascin-C by enzyme-linked immunosorbent assay. We examined the expression of tenascins and type V collagen in skin by immunohistochemical methods and sequenced the tenascin-X gene., Results: Tenascin-X was present in serum from all normal subjects, all patients with psoriasis, all patients with rheumatoid arthritis, and 146 of 151 patients with the Ehlers-Danlos syndrome. Tenascin-X was absent from the serum of the 5 remaining patients with Ehlers-Danlos syndrome, who were unrelated. Tenascin-X deficiency was confirmed in these patients by analysis of skin fibroblasts and by immunostaining of skin. The expression of tenascin-C and type V collagen was normal in these patients. All five of these patients had hypermobile joints, hyperelastic skin, and easy bruising, without atrophic scarring. Tenascin-X mutations were identified in all tenascin-X-deficient patients; one patient had a homozygous tenascin-X gene deletion, one was heterozygous for the deletion, and three others had homozygous truncating point mutations, confirming a causative role for tenascin-X and a recessive pattern of inheritance., Conclusions: Tenascin-X deficiency causes a clinically distinct, recessive form of the Ehlers-Danlos syndrome. This finding indicates that factors other than the collagens or collagen-processing enzymes can cause the syndrome and suggests a central role for tenascin-X in maintaining the integrity of collagenous matrix.

Introduction: Tenascin-X (TNX) is an extracellular matrix (ECM) glycoprotein, the absence of which in humans leads to a recessive form of Ehlers-Danlos syndrome (EDS), a group of inherited connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. A mouse model of TNX-deficient type EDS has been used to characterize the dermatological, orthopedic, and obstetrical features. The growing insight in the clinical overlap between myopathies and inherited connective tissue disorders asks for a study of the muscular characteristics of inherited connective tissue diseases. Therefore, this study aims to define the muscular phenotype of TNX knockout (KO) mice. Materials and methods: We performed a comprehensive study on the muscular phenotype of these TNX KO mice, consisting of standardized clinical assessment, muscle histology, and gene expression profiling of muscle tissue. Furthermore, peripheral nerve composition was studied by histology and electron microscopy. Results: The main findings are the presence of mild muscle weakness, mild myopathic features on histology, and functional upregulation of genes encoding proteins involved in ECM degradation and synthesis. Additionally, sciatic nerve samples showed mildly reduced collagen fibril density of endoneurium. Discussion: The muscular phenotype of TNX KO mice consists of mild muscle weakness with histological signs of myopathy and of increased turnover of the ECM in muscle. Furthermore, mildly reduced diameter of myelinated fibers and reduction of collagen fibril density of endoneurium may correspond with polyneuropathy in TNX-deficient EDS patients. This comprehensive assessment can serve as a starting point for further investigations on neuromuscular function in TNX KO mice. [ABSTRACT FROM AUTHOR]

We analysed the diversity of tenascin-X (TNX) species in serum and studied parameters that could affect determination of TNX levels in serum. Using western blot analysis we identified at least seven distinct TNX species, ranging from 75 kDa to the presumably full-length 450 kDa form. Purification of serum TNX followed by sequence analysis positively identified two major TNX species of 75 and 140 kDa. We found that serum TNX binds to tropoelastin but not to fibrillar collagens. We conclude that serum TNX is composed of distinct molecular species that retain functional activity. [ABSTRACT FROM AUTHOR]

Abstract: This review presents an overview of myopathies and inherited connective tissue disorders that are caused by defects in or deficiencies of molecules within the extracellular matrix (ECM). We will cover the myopathies caused by defects in transmembrane protein complexes (dystroglycan, sarcoglycan, and integrins), laminin, and collagens (collagens VI, XIII, and XV). Clinical characteristics of several of these myopathies imply skin and joint features. We subsequently describe the inherited connective tissue disorders that are characterized by mild to moderate muscle involvement in addition to the dermal, vascular, or articular symptoms. These disorders are caused by defects of matrix-embedded ECM molecules that are also present within muscle (collagens I, III, V, IX, lysylhydroxylase, tenascin, fibrillin, fibulin, elastin, and perlecan). By focussing on the structure and function of these ECM molecules, we aim to point out the clinical and molecular overlap between the groups of disorders. We argue that clinicians and researchers dealing with myopathies and inherited connective tissue disorders should be aware of this overlap. Only a multi-disciplinary approach will allow full recognition of the wide variety of symptoms present in the spectrum of ECM defects, which has important implications for scientific research, diagnosis, and for the treatment of these disorders. [Copyright &y& Elsevier]