Quantitative measurement of urinary glycosaminoglycans using a modified DMB method facilitates the diagnosis and monitoring of mucopolysaccharidoses

Abstract

Mucopolysaccharidoses (MPS) are a heterogeneous group of inherited lysosomal storage disorders (LSDs), due to impaired breakdown of glycosaminoglycans (GAGs), resulting from dysfunctional lysosomal acid hydrolases. Determination of urinary GAG content is a first-line screening assay for MPS. We modified and evaluated a quantitative colorimetric method based on 1,9 Dimethyl-Methylene Blue (DMB) and were able to identify seven new pediatric cases of MPS within a year and subsequently confirmed them by enzymatic analysis. In addition, three cases with borderline urinary GAG content were subsequently diagnosed with other LSDs. We monitored a child with MPS III (Sanfilippo) type C treated with genistein at a dose of 5 mg/kg/day for over a year and we found no change in urine GAG content. In conclusion: the modified DMB colorimetric method is an, accurate and convenient method for measuring urinary GAGs content and facilitates the diagnosis and monitoring of MPS.