Proton Nuclear Magnetic Resonance Spectroscopic Detection of Sialic Acid Storage Disease

Abstract

Sialic acid storage disease (SASD) is a rare autosomal recessive lysosomal storage disorder characterized by excessive urinary excretion of free sialic acid and an accumulation of free sialic acid in skin fibroblasts (1). Clinically, two major forms exist: an infantile type with severe progression leading to early death (2), and a milder form (Salla disease) with a protracted course (3). The basic defect in both forms is a malfunction of a sialic acid transporter in the lysosomal membrane (4). Because the clinical characteristics of SASD are very similar to those of other lysosomal storage diseases, differential diagnosis relies on detection of increased urinary sialic acid excretion by thin-layer chromatography of urine (5) and quantification by colorimetric analysis (6) or ion-exchange HPLC (7). However, each method has disadvantages. Colorimetric assays suffer from interference by 2-deoxyglucose, whereas HPLC methods require lengthy sample preparation. Proton nuclear magnetic resonance (1H-NMR) spectroscopy is a powerful tool for the structural elucidation and characterization of body fluid metabolites in inherited metabolic disorders (8)(9)(10)(11). The technique is rapid, requiring minimal sample treatment. Sialic acid (free and as a conjugate) has been extracted from the urine of individuals with SASD and sialidoses, respectively, and characterized by 1H-NMR spectroscopy (12)(13)(14); however, the technique has not been used for direct diagnosis from unextracted urine. We carried out 1H-NMR analysis of urine from five patients with SASD (two with the infantile form, one with the intermediate form, and two patients with Salla disease) and compared the urinary sialic acid excretion determined by colorimetric analysis and 1H-NMR spectroscopy. Urine samples from patients with SASD were obtained as part of a selective screening program for inborn errors of metabolism. Clinical and diagnostic data on three patients have been described …