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FIRST DEMONSTRATION OF A STRUCTURAL MUTATION OF PROCOLLAGEN IN A PATIENT WITH EHLERS-DANLOS SYNDROME (EDS): 69

Three patients with severe hypermobility of the joints but only mild hyperelasticity of the skin were previously reported (Science 182,298-300,1973) to have partial deficiency of procollagen N-protease, one of the two enzymes necessary for the conversion of procollagen to collagen. One 9 year old patient was reinvestigated. In a biopsy sample of her skin, collagen was more extractable in neutral 0.5 M NaCl containing protease inhibitors. In addition to the normally occurring αl- and α2-chains, α2-precursor chains (pNα2), but no pNαl were detected by SDS-PAGE. Digestion of the collagen with animal collagenase generated the three N-terminal fragments αlA, α2A and pNα2A but only the two normally occurring C-terminal fragments αlB and α2B. Digestion of the extracts with purified procollagen N-protease did not remove the N-propeptide from the pNα2 chains. This excluded the possibility of incomplete conversion of pN-collagen owing to partial procollagen N-protease deficiency. The findings were corroborated by the study of radio-active procollagen produced by cultured skin fibroblasts. The latter had normal N-protease. Results suggested that the proα2-chains had a structural defect near the N-protease cleavage site preventing the enzymatic removal of the N-propeptide. Since equal amounts of pNα2- and α2-chains were produced, gene dosage was evidenced in this sporadic case of EDS probably caused by a new mutation.