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Musculocontractural Ehlers-Danlos syndrome (mcEDS) is a subtype of EDS caused by mutations in the gene for carbohydrate sulfotransferase 14 (CHST14) (mcEDS-CHST14) or dermatan sulfate epimerase (DSE) (mcEDS-DSE). These mutations induce loss of enzymatic activity in D4ST1 or DSE and disrupt dermatan sulfate (DS) biosynthesis. The depletion of DS causes the symptoms of mcEDS, such as multiple congenital malformations (e.g., adducted thumbs, clubfeet, and craniofacial characteristics) and progressive connective tissue fragility-related manifestations (e.g., recurrent dislocations, progressive talipes or spinal deformities, pneumothorax or pneumohemothorax, large subcutaneous hematomas, and/or diverticular perforation). Careful observations of patients and model animals are important to investigate pathophysiological mechanisms and therapies for the disorder. Some independent groups have investigated Chst14 gene-deleted (Chst14^-/-) and Dse^-/- mice as models of mcEDS-CHST14 and mcEDS-DSE, respectively. These mouse models exhibit similar phenotypes to patients with mcEDS, such as suppressed growth and skin fragility with deformation of the collagen fibrils. Mouse models of mcEDS-CHST14 also show thoracic kyphosis, hypotonia, and myopathy, which are typical complications of mcEDS. These findings suggest that the mouse models can be useful for research uncovering the pathophysiology of mcEDS and developing etiology-based therapy. In this review, we organize and compare the data of patients and model mice. Full article

Musculocontractural Ehlers–Danlos Syndome (mcEDS) is a type of EDS caused by biallelic pathogenic variants in the gene for carbohydrate sulfotransferase 14/dermatan 4-O-sulfotransferase 1 (CHST14/D4ST1, mcEDS-CHST14), or in the gene for dermatan sulfate epimerase (DSE, mcEDS-DSE). Thus far, 41 patients from 28 families with mcEDS-CHST14 and five patients from four families with mcEDS-DSE have been described in the literature. Clinical features comprise multisystem congenital malformations and progressive connective tissue fragility-related manifestations. This review outlines recent advances in understanding the pathophysiology of mcEDS. Pathogenic variants in CHST14 or DSE lead to reduced activities of relevant enzymes, resulting in a negligible amount of dermatan sulfate (DS) and an excessive amount of chondroitin sulfate. Connective tissue fragility is presumably attributable to a compositional change in the glycosaminoglycan chains of decorin, a major DS-proteoglycan in the skin that contributes to collagen fibril assembly. Collagen fibrils in affected skin are dispersed in the papillary to reticular dermis, whereas those in normal skin are regularly and tightly assembled. Glycosaminoglycan chains are linear in affected skin, stretching from the outer surface of collagen fibrils to adjacent fibrils; glycosaminoglycan chains are curved in normal skin, maintaining close contact with attached collagen fibrils. Homozygous (Chst14^−/−) mice have been shown perinatal lethality, shorter fetal length and vessel-related placental abnormalities. Milder phenotypes in mcEDS-DSE might be related to a smaller fraction of decorin DS, potentially through residual DSE activity or compensation by DSE2 activity. These findings suggest critical roles of DS and DS-proteoglycans in the multisystem development and maintenance of connective tissues, and provide fundamental evidence to support future etiology-based therapies. Full article