Background: Pseudoxanthoma elasticum (PXE) is a hereditary connective tissue disease in which proteoglycans have altered properties. We investigated whether altered proteoglycan metabolism occurs in vivo and may be reflected in the urine of PXE individuals by analyzing the excreted polysaccharides.
Methods: We measured sulfated glycosaminoglycans in the urine of 10 PXE-affected patients, 12 healthy carriers, and 20 healthy controls by agarose gel electrophoresis. Chondroitin sulfate and heparan sulfate disaccharides were also quantified by treatment with specific lyases and separation of products by chromatography.
Results: Total polysaccharides were 34% lower in the urine of PXE-affected patients and 17% lower in healthy carriers than in the control group. Chondroitin sulfate was significantly (P <0.01) decreased, and heparan sulfate was significantly increased. The ratio of chondroitin sulfate to heparan sulfate was 2.7 for PXE-affected patients, 2.3 for healthy carriers, and 10.7 for controls. In PXE-affected individuals and carriers, chondroitin sulfate contained more 4-sulfated disaccharide, less 6-sulfated disaccharide, and decreased nonsulfated disaccharide. Heparan sulfate from PXE-affected individuals and healthy carriers produced significantly less N-sulfated disaccharide and more disaccharide sulfated at the C-6 position with no significant abnormality of the nonsulfated disaccharide percentage and sulfates:disaccharide ratio.
Conclusions: The urinary data support the concept that the inherited defect of the ABCC6/MRP6 transporter in PXE alters metabolism of key polysaccharides. Structural analysis of urinary sulfated polyanions may be useful in the diagnosis of PXE.