Reliable detection of mucopolysacchariduria in dried-urine filter paper samples

Background: The mucopolysaccharidoses (MPS) are inherited metabolic disorders with bone, joint, and visceral abnormalities, leading to multi-organ dysfunction and, sometimes, neurological manifestations. These diseases are caused by storage of glycosaminoglycans (GAGs) and other complex molecules in tissues, among other pathogenic mechanisms. Definitive diagnosis of the affected individual is mainly based on the identification of the specific enzyme deficiency. New therapies are available or are in development for these pathologies, and early diagnosis seems to be important for the therapy outcomes. Almost all MPS patients have increased levels of GAGs in urine being their evaluation usually the first step in the screening of these conditions. Test on urine may be challenging as transportation of liquid urine samples in appropriate conditions for long distances, especially across international borders, could be difficult.

Methods: With the aim of overcoming the difficulties related to the use of liquid samples, we extended and validated previous studies about colorimetric determination of GAGs in dried-urine filter paper (DUFP) samples.

Results: In the conditions we described, there are no differences in the concentration of GAGs between urine and DUFP samples. Untreated patients with MPS and normal controls were well discriminated using any of the samples.

Conclusions: Dried-urine filter paper is a suitable sample for the colorimetric quantitation of GAGs, and that its incorporation as an additional tool for screening of MPS should be considered by reference laboratories.