Transforming growth factor-β (TGF-β) pathway abnormalities in tenascin-X deficiency associated with CAH-X syndrome

Patients with congenital adrenal hyperplasia (CAH) with tenascin-X deficiency (CAH-X syndrome) have both endocrine imbalances and characteristic Ehlers Danlos syndrome phenotypes. Unlike other subtypes, tenascin-X-related Ehlers Danlos syndrome is caused by an extracellular matrix protein deficiency rather than a defect in fibrillar collagen or a collagen-modifying enzyme, and the understanding of the disease mechanisms is limited. We hypothesized that transforming growth factor-β pathway dysregulation may, in part, be responsible for connective tissue phenotypes observed in CAH-X, due to this pathway's known role in connective tissue disorders. Fibroblasts and direct tissue from human skin biopsies from CAH-X probands and age- and sex-matched controls were screened for transforming growth factor-β biomarkers known to be dysregulated in other hereditary disorders of connective tissue. In CAH-X fibroblast lines and dermal tissue, pSmad1/5/8 was significantly upregulated compared to controls, suggesting involvement of the bone morphogenetic protein pathway. Additionally, CAH-X samples compared to controls exhibited significant increases in fibroblast-secreted TGF-β3, a cytokine important in secondary palatal development, and in plasma TGF-β2, a cytokine involved in cardiac function and development, as well as palatogenesis. Finally, MMP-13, a matrix metalloproteinase important in secondary palate formation and tissue remodeling, had significantly increased mRNA and protein expression in CAH-X fibroblasts and direct tissue. Collectively, these results demonstrate that patients with CAH-X syndrome exhibit increased expression of several transforming growth factor-β biomarkers and provide a novel link between this signaling pathway and the connective tissue dysplasia phenotypes associated with tenascin-X deficiency.