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 five 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.
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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.