Abstract
Background: The development of therapies for lysosomal storage disorders has created a need for biochemical markers to monitor the efficacy of therapy and methods to quantify these markers in biologic samples. In Pompe disease, the concentration of a tetrasaccharide, consisting of four glucose residues, is reputedly increased in urine and plasma, but faster and more sensitive methods are required for the analysis of this, and other oligosaccharides, from biologic fluids.
Methods: We optimized the derivatization of storage oligosaccharides with 1-phenyl-3-methyl-5-pyrazolone for the measurement, by electrospray ionization tandem mass spectrometry, of oligosaccharide concentrations in urine (n = 6), plasma (n = 11), and dried-blood spots (n = 17) from Pompe-affected individuals. Age-matched control samples of urine (n = 10), plasma (n = 28), and blood spots (n = 369) were also analyzed.
Results: The mean tetrasaccharide concentration was increased in urine from infantile-onset (0.69–12 mmol/mol of creatinine) and adult-onset (0.22–3.0 mmol/mol of creatinine) Pompe individuals compared with age-matched controls. In plasma samples, an increased tetrasaccharide concentration was observed in some infantile patients (up to 22 μmol/L) compared with age-matched controls (mean, 2.2 μmol/L). The method developed was sensitive enough to determine oligosaccharide concentrations in a single 3-mm blood spot, but no differences were observed between blood spots from control and Pompe-affected individuals.
Conclusions: Measurements of oligosaccharide concentrations in urine by this new method have potential application for the diagnosis and monitoring of patients with Pompe disease. Plasma analysis may have limited application for infantile patients, but analysis of blood spots does not discriminate between controls and affected individuals.
Direct multiplex assay of enzymes in dried blood spots by tandem mass spectrometry for the newborn screening of lysosomal storage disorders
