Profiling oligosaccharidurias by electrospray tandem mass spectrometry: Quantifying reducing oligosaccharides

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Analysis of Urinary Oligosaccharides and Glycoamino Acids for the Diagnosis of Mucopolysaccharidosis and Glycoproteinosis

BACKGROUND

Mucopolysaccharidosis (MPS) and glycoproteinosis are 2 groups of heterogenous lysosomal storage disorders (LSDs) caused by defective degradation of glycosaminoglycans (GAGs) and glycoproteins, respectively. Oligosaccharides and glycoamino acids have been recognized as biomarkers for MPS and glycoproteinosis. Given that both groups of LSDs have overlapping clinical features, a multiplexed assay capable of unambiguous subtyping is desired for accurate diagnosis, and potentially for severity stratification and treatment monitoring.

METHODS

Urinary oligosaccharides were derivatized with 3-methyl-1-phenyl-2-pyrazoline-5-one (PMP) and analyzed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) together with the underivatized glycoamino acids. Novel biomarkers were identified with a semi-targeted approach with precursor mass scanning, the fragmentation pattern (if applicable), and the biochemical basis of the condition.

RESULTS

A UPLC-MS/MS analysis with improved chromatographic separation was developed. Novel biomarkers for MPS-IIIA, IIIB, IIIC, and VII were identified and validated. A total of 28 oligosaccharides, 2 glycoamino acids, and 2 ratios were selected as key diagnostic biomarkers. Validation studies including linearity, lower limit of quantitation (LLOQ), and precision were carried out with the assay performance meeting the required criteria. Age-specific reference ranges were collected. In the 76 untreated patients, unambiguous diagnosis was achieved with 100% sensitivity and specificity. Additionally, the levels of disease-specific biomarkers were substantially reduced in the treated patients.

CONCLUSIONS

A multiplexed UPLC-MS/MS assay for urinary oligosaccharides and glycoamino acids measurement was developed and validated. The assay is suitable for the accurate diagnosis and subtyping of MPS and glycoproteinosis, and potentially for severity stratification and monitoring response to treatment.

A pentasaccharide for monitoring pharmacodynamic response to gene therapy in GM1 gangliosidosis

BACKGROUND

GM1 gangliosidosis is a rare, fatal, neurodegenerative disease caused by mutations in the GLB1 gene and deficiency in β-galactosidase. Delay of symptom onset and increase in lifespan in a GM1 gangliosidosis cat model after adeno-associated viral (AAV) gene therapy treatment provide the basis for AAV gene therapy trials. The availability of validated biomarkers would greatly improve assessment of therapeutic efficacy.

METHODS

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to screen oligosaccharides as potential biomarkers for GM1 gangliosidosis. The structures of pentasaccharide biomarkers were determined with mass spectrometry, as well as chemical and enzymatic degradations. Comparison of LC-MS/MS data of endogenous and synthetic compounds confirmed the identification. The study samples were analyzed with fully validated LC-MS/MS methods.

FINDINGS

We identified two pentasaccharide biomarkers, H3N2a and H3N2b, that were elevated more than 18-fold in patient plasma, cerebrospinal fluid (CSF), and urine. Only H3N2b was detectable in the cat model, and it was negatively correlated with β-galactosidase activity. Following intravenous (IV) AAV9 gene therapy treatment, reduction of H3N2b was observed in central nervous system, urine, plasma, and CSF samples from the cat model and in urine, plasma, and CSF samples from a patient. Reduction of H3N2b accurately reflected normalization of neuropathology in the cat model and improvement of clinical outcomes in the patient.

INTERPRETATIONS

These results demonstrate that H3N2b is a useful pharmacodynamic biomarker to evaluate the efficacy of gene therapy for GM1 gangliosidosis. H3N2b will facilitate the translation of gene therapy from animal models to patients.

FUNDING

This work was supported by grants U01NS114156, R01HD060576, ZIAHG200409, and P30 DK020579 from the National Institutes of Health (NIH) and a grant from National Tay-Sachs and Allied Diseases Association Inc.

Analysis of urinary oligosaccharide excretion patterns by UHPLC/HRAM mass spectrometry for screening of lysosomal storage disorders

Oligosaccharidoses, sphingolipidoses and mucolipidoses are lysosomal storage disorders (LSDs) in which defective breakdown of glycan-side chains of glycosylated proteins and glycolipids leads to the accumulation of incompletely degraded oligosaccharides within lysosomes. In metabolic laboratories, these disorders are commonly diagnosed by thin-layer chromatography (TLC) but more recently also mass spectrometry-based approaches have been published. To expand the possibilities to screen for these diseases, we developed an ultra-high-performance liquid chromatography (UHPLC) with a high-resolution accurate mass (HRAM) mass spectrometry (MS) screening platform, together with an open-source iterative bioinformatics pipeline. This pipeline generates comprehensive biomarker profiles and allows for extensive quality control (QC) monitoring. Using this platform, we were able to identify α-mannosidosis, β-mannosidosis, α-N-acetylgalactosaminidase deficiency, sialidosis, galactosialidosis, fucosidosis, aspartylglucosaminuria, GM1 gangliosidosis, GM2 gangliosidosis (M. Sandhoff) and mucolipidosis II/III in patient samples. Aberrant urinary oligosaccharide excretions were also detected for other disorders, including NGLY1 congenital disorder of deglycosylation, sialic acid storage disease, MPS type IV B and GSD II (Pompe disease). For the latter disorder, we identified heptahexose (Hex7), as a potential urinary biomarker, in addition to glucose tetrasaccharide (Glc4), for the diagnosis and monitoring of young onset cases of Pompe disease. Occasionally, so-called "neonate" biomarker profiles were observed in young patients, which were probably due to nutrition. Our UHPLC/HRAM-MS screening platform can easily be adopted in biochemical laboratories and allows for simple and robust screening and straightforward interpretation of the screening results to detect disorders in which aberrant oligosaccharides accumulate.

Detecting lysosomal storage disorders by glycomic profiling using liquid chromatography mass spectrometry

BACKGROUND

Urine and plasma biomarker testing for lysosomal storage disorders by liquid chromatography mass spectrometry (LC-MS) currently requires multiple analytical methods to detect the abnormal accumulation of oligosaccharides, mucopolysaccharides, and glycolipids. To improve clinical testing efficiency, we developed a single LC-MS method to simultaneously identify disorders of oligosaccharide, mucopolysaccharide, and glycolipid metabolism with minimal sample preparation.

METHODS

We created a single chromatographic method for separating free glycans and glycolipids in their native form, using an amide column and high pH conditions. We used this glycomic profiling method both in untargeted analyses of patient and control urines using LC ion-mobility high-resolution MS (biomarker discovery), and targeted analyses of urine, serum, and dried blood spot samples by LC-MS/MS (clinical validation).

RESULTS

Untargeted glycomic profiling revealed twenty biomarkers that could identify and subtype mucopolysaccharidoses. We incorporated these with known oligosaccharide and glycolipid biomarkers into a rapid test that identifies at least 27 lysosomal storage disorders, including oligosaccharidoses, mucopolysaccharidoses, sphingolipidoses, glycogen storage disorders, and congenital disorders of glycosylation and de-glycosylation. In a validation set containing 115 urine samples from patients with lysosomal storage disorders, all were unambiguously distinguished from normal controls, with correct disease subtyping for 88% (101/115) of cases. Glucosylsphingosine was reliably elevated in dried blood spots from Gaucher disease patients with baseline resolution from galactosylsphingosine.

CONCLUSION

Glycomic profiling by liquid chromatography mass spectrometry identifies a range of lysosomal storage disorders. This test can be used in clinical evaluations to rapidly focus a diagnosis, as well as to clarify or support additional gene sequencing and enzyme studies.

A new UHPLC-MS/MS method for the screening of urinary oligosaccharides expands the detection of storage disorders

Background

Oligosaccharidoses are storage disorders due to enzymatic defects involved in the breakdown of the oligosaccharidic component of glycosylated proteins. The defect cause the accumulation of oligosaccharides (OS) and, depending on the lacking enzyme, results in characteristic profiles which are helpful for the diagnosis. We developed a new tandem mass spectrometry method for the screening of urinary OS which was applied to identify a large panel of storage disorders.

Methods

The method was set-up in urine and dried urine spots (DUS). Samples were analysed, without derivatization and using maltoheptaose as internal standard, by UHPLC-MS/MS with MRM acquisition of target OS transitions, including Glc4, the biomarker of Pompe disease. The chromatographic run was < 30 min. Samples from patients with known storage disorders were used for clinical validation.

Results

The method allowed to confirm the diagnosis of oligosaccharidoses (sialidosis, α-/β-mannosidosis, fucosidosis, aspartylglucosaminuria) and of GM1 and GM2 (Sandhoff type) gangliosidosis, by detecting specific OS profiles. In other storage disorders (mucolipidosis II and III, mucopolysaccharidosis type IVB) the analyisis revealed abnormal OS excretion with non-specific profiles. Besides Pompe disease, the tetrasaccharide Glc4 was increased also in disorders of autophagy (Vici syndrome, Yunis-Varon syndrome, and Danon disease) presenting cardiomuscular involvement with glycogen storage. Overall, results showed a clear separation between patients and controls, both in urine and in DUS.

Conclusion

This new UHPLC/MS-MS method, which is suitable for rapid and easy screening of OS in urine and DUS, expands the detection of storage disorders from oligosaccharidoses to other diseases, including the novel category of inherited disorders of autophagy.

Characterization of glycan substrates accumulating in GM1 Gangliosidosis

Introduction

GM1 gangliosidosis is a rare autosomal recessive genetic disorder caused by the disruption of the GLB1 gene that encodes β-galactosidase, a lysosomal hydrolase that removes β-linked galactose from the non-reducing end of glycans. Deficiency of this catabolic enzyme leads to the lysosomal accumulation of GM1 and its asialo derivative GA1 in β-galactosidase deficient patients and animal models. In addition to GM1 and GA1, there are other glycoconjugates that contain β-linked galactose whose metabolites are substrates for β-galactosidase. For example, a number of N-linked glycan structures that have galactose at their non-reducing end have been shown to accumulate in GM1 gangliosidosis patient tissues and biological fluids.

Objective

In this study, we attempt to fully characterize the broad array of GLB1 substrates that require GLB1 for their lysosomal turnover.

Results

Using tandem mass spectrometry and glycan reductive isotope labeling with data-dependent mass spectrometry, we have confirmed the accumulation of glycolipids (GM1 and GA1) and N-linked glycans with terminal beta-linked galactose. We have also discovered a novel set of core 1 and 2 O-linked glycan metabolites, many of which are part of structurally-related isobaric series that accumulate in disease. In the brain of GLB1 null mice, the levels of these glycan metabolites increased along with those of both GM1 and GA1 as a function of age. In addition to brain tissue, we found elevated levels of both N-linked and O-linked glycan metabolites in a number of peripheral tissues and in urine. Both brain and urine samples from human GM1 gangliosidosis patients exhibited large increases in steady state levels for the same glycan metabolites, demonstrating their correlation with this disease in humans as well.

Conclusions

Our studies illustrate that GLB1 deficiency is not purely a ganglioside accumulation disorder, but instead a broad oligosaccharidosis that include representatives of many β-linked galactose containing glycans and glycoconjugates including glycolipids, N-linked glycans, and various O-linked glycans. Accounting for all β-galactosidase substrates that accumulate when this enzyme is deficient increases our understanding of this severe disorder by identifying metabolites that may drive certain aspects of the disease and may also serve as informative disease biomarkers to fully evaluate the efficacy of future therapies.

UPLC-MS/MS Analysis of Urinary Free Oligosaccharides for Lysosomal Storage Diseases: Diagnosis and Potential Treatment Monitoring

BACKGROUND

The glycoproteinoses are a subgroup of lysosomal storage diseases (LSDs) resulting from impaired degradation of N-linked oligosaccharide side chains of glycoproteins, which are commonly screened by detecting the accumulated free oligosaccharides (FOSs) in urine via thin layer chromatography (TLC). The traditional TLC method suffers from limited analytical sensitivity and specificity and lacks quantification capability. Therefore, we developed an analytically sensitive and relatively specific assay using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for urinary FOS analysis and validated its use for urine screening of glycoproteinoses and other LSDs.

METHODS

Urine volumes equivalent to 30 μg of creatinine were derivatized with butyl-4-aminobenzoate and then purified through a solid-phase extraction cartridge. A 7-min UPLC-MS/MS analysis was performed on a triple quadrupole mass spectrometer using an amide column for separation of derivatized FOS. Urine samples from >100 unaffected controls and 37 patients with various LSDs were studied.

RESULTS

Relative quantification was conducted on 7 selected FOSs using a single internal standard, which allowed the identification of patients with 1 of 8 different LSDs: aspartylglucosaminuria, α-fucosidosis, α-mannosidosis, β-mannosidosis, β-galactosidase deficiency, Sandhoff disease, sialidosis, and galactosialidosis. Patients treated with hematopoietic stem cell transplant show decreased FOS responses compared with untreated patients.

CONCLUSIONS

This UPLC-MS/MS assay offers a valuable tool for screening of glycoproteinoses and other LSDs, with potential use for future treatment monitoring.

Contribution of tandem mass spectrometry to the diagnosis of lysosomal storage disorders

Tandem mass spectrometry (MS/MS) is a highly sensitive and specific technique. Thanks to the development of triple quadrupole analyzers, it is becoming more widely used in laboratories working in the field of inborn errors of metabolism. We review here the state of the art of this technique applied to the diagnosis of lysosomal storage disorders (LSDs) and how MS/MS has changed the diagnostic rationale in recent years. This fine technology brings more sensitive, specific, and reliable methods than the previous biochemical ones for the analysis of urinary glycosaminoglycans, oligosaccharides, and sialic acid. In sphingolipidoses, the quantification of urinary sphingolipids (globotriaosylceramide, sulfatides) is possible. The measurement of new plasmatic biomarkers such as oxysterols, bile acids, and lysosphingolipids allows the screening of many sphingolipidoses and related disorders (Niemann-Pick type C), replacing tedious biochemical techniques. Applied to amniotic fluid, a more reliable prenatal diagnosis or screening of LSDs is now available for fetuses presenting with antenatal manifestations. Applied to enzyme measurements, it allows high throughput assays for the screening of large populations, even newborn screening. The advent of this new method can modify the diagnostic rationale behind LSDs.

Development of a new tandem mass spectrometry method for urine and amniotic fluid screening of oligosaccharidoses

RATIONALE

The first step in the diagnosis of oligosaccharidoses is to evidence abnormal oligosaccharides excreted in urine, usually performed by the poorly sensitive but efficient thin layer chromatography (TLC) method. Developing a tandem mass spectrometry (MS/MS) technique could be of great interest to replace TLC.

METHODS

Abnormal underivatized oligosaccharides have been recently studied using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, allowing the unambiguous identification of oligosaccharidoses. Based on this previous work, we developed an advantageous and efficient liquid chromatography (LC)/MS/MS method using a more common triple quadrupole tandem mass spectrometer for oligosaccharides analysis.

RESULTS

Oligosaccharidoses (n = 97) and control (n = 240) urine samples were analysed. A specific pattern was obtained for each oligosaccharidosis using this method. In urine, it allows not only the identification of all the oligosaccharidoses previously identified by TLC (fucosidosis, alphamannosidosis, aspartylglucosaminuria, GM1 gangliosidosis, sialidosis, galactosialidosis and Schindler disease), but also extends the field of diagnosis to mucolipidosis type II, Sandhoff disease, and β-mannosidosis. The same technique was applied to 16 amniotic fluid supernatants from oligosaccharidosis-affected foetuses (n = 16) compared with 37 unaffected. All the affected foetuses could be clearly identified: sialidosis (n = 3), galactosialidosis (n = 4), aspartylglucosaminuria (n = 1), mucolipidosis type II (n = 4) or GM1 gangliosidosis (n = 4). This technique can be applied to early prenatal diagnosis as well as to the oligosaccharidosis screening in the case of non-immune hydrops fetalis.

CONCLUSIONS

The method is quick and easy to run, with an LC analysis time of 13 min per sample. The quantitative validation could not be obtained in the absence of a specific standard and of a labelled internal standard for each compound. Even if this LC/MS/MS method is only qualitative, it is very specific and much more sensitive than TLC. It allows the urinary screening of oligosaccharidoses, even mild or late-onset forms, and the screening of antenatal forms in amniotic fluid. Copyright © 2017 John Wiley & Sons, Ltd.

Lysosomal diseases: diagnostic update

Technological developments in newborn and population screening, biomarker discovery for monitoring treatment and rapid high throughput DNA sequencing are having a great impact on the diagnostic procedure for symptomatic patients with lysosomal storage diseases. The use of dried blood spots, initially for newborn screening, has stimulated the introduction of automated, rapid and more sensitive methods for the assay of lysosomal enzymes, including the synthesis of novel substrates. Storage products and secondary metabolites in urine and cells can be identified and measured very accurately and sensitively by high performance liquid chromatography and tandem mass spectrometry. This has enhanced the preliminary metabolite screen for LSDs and facilitated the diagnosis of transport defects. Fast, reliable and affordable high throughput DNA sequencing, such as whole or selected exome sequencing, is helping to make diagnoses in difficult cases, to reveal novel gene defects, to widen the clinical spectrum of diseases and possibly to identify modifying genetic factors. Bioinformatics will be necessary to handle the data generated by these new technologies. Notwithstanding, these technical innovations, accurate and reliable diagnosis will still depend on the knowledge and experience of skilled laboratory staff.

Fast urinary screening of oligosaccharidoses by MALDI-TOF/TOF mass spectrometry

Background

Oligosaccharidoses, which belong to the lysosomal storage diseases, are inherited metabolic disorders due to the absence or the loss of function of one of the enzymes involved in the catabolic pathway of glycoproteins and indirectly of glycosphingolipids. This enzymatic deficiency typically results in the abnormal accumulation of uncompletely degraded oligosaccharides in the urine. Since the clinical features of many of these disorders are not specific for a single enzyme deficiency, unambiguous screening is critical to limit the number of costly enzyme assays which otherwise must be performed.

Methods

Here we provide evidence for the advantages of using a MALDI-TOF/TOF (matrix-assisted laser desorption ionization time-of-flight) mass spectrometric (MS) method for screening oligosaccharidoses. Urine samples from previously diagnosed patients or from unaffected subjects were randomly divided into a training set and a blind testing set. Samples were directly analyzed without prior treatment.

Results

The characteristic MS and MS/MS molecular profiles obtained allowed us to identify fucosidosis, aspartylglucosaminuria, GM1 gangliosidosis, Sandhoff disease, α-mannosidosis, sialidosis and mucolipidoses type II and III.

Conclusions

This method, which is easily run in less than 30 minutes, is performed in a single step, and is sensitive and specific. Invaluable for clinical chemistry purposes this MALDI-TOF/TOF mass spectrometry procedure is semi-automatizable and suitable for the urinary screening of oligosacharidoses.

Oligosaccharide analysis in urine by maldi-tof mass spectrometry for the diagnosis of lysosomal storage diseases

BACKGROUND

There are 45 known genetic diseases that impair the lysosomal degradation of macromolecules. The loss of a single lysosomal hydrolase leads to the accumulation of its undegraded substrates in tissues and increases of related glycoconjugates in urine, some of which can be detected by screening of free oligosaccharides (FOS) in urine. Traditional 1-dimensional TLC for urine oligosaccharide analysis has limited analytical specificity and sensitivity. We developed fast and robust urinary FOS and glycoaminoacid analyses by MALDI-time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry for the diagnosis of oligosaccharidoses and other lysosomal storage diseases.

METHODS

The FOS in urine equivalent to 0.09 mg creatinine were purified through sequential passage over a Sep-Pak C18 column and a carbograph column and were then permethylated. MALDI-TOF/TOF was used to analyze the permethylated FOS. We studied urine samples from individuals in 7 different age groups ranging from 0-1 months to ≥ 17 years as well as urine from known patients with different lysosomal storage diseases.

RESULTS

We identified diagnostic urinary FOS patterns for α-mannosidosis, galactosialidosis, mucolipidosis type II/III, sialidosis, α-fucosidosis, aspartylglucosaminuria (AGU), Pompe disease, Gaucher disease, and GM1 and GM2 gangliosidosis. Interestingly, the increase in urinary FOS characteristic of lysosomal storage diseases relative to normal FOS appeared to correlate with the disease severity.

CONCLUSIONS

The analysis of urinary FOS by MALDI-TOF/TOF is a powerful tool for first-tier screening of oligosaccharidoses and lysosomal storage diseases.

Glycosaminoglycan glycomics using mass spectrometry

The fact that sulfated glycosaminoglycans (GAGs) are necessary for the functioning of all animal physiological systems drives the need to understand their biology. This understanding is limited, however, by the heterogeneous nature of GAG chains and their dynamic spatial and temporal expression patterns. GAGs have a regulated structure overlaid by heterogeneity but lack the detail necessary to build structure/function relationships. In order to provide this information, we need glycomics platforms that are sensitive, robust, high throughput, and information rich. This review summarizes progress on mass-spectrometry-based GAG glycomics methods. The areas covered include disaccharide analysis, oligosaccharide profiling, and tandem mass spectrometric sequencing.

Determination of sialylated and neutral oligosaccharides in urine by mass spectrometry

This protocol describes a method to allow for the detection of specific oligosaccharide fragments in urine by tandem mass spectrometry. The detection of fragments with specific masses indicates the presence of one of a number of diseases where the deficiency of lysosomal enzymes involved in the degradation of the glyco- moieties of glycoproteins is present in the patient. This method describes the derivatization of oligosaccharides present in urine with phenyl-1-methylpyrazolone, which renders them hydrophobic, thus allowing desalting with Combi cleanup columns prior to injection. This method allows the detection of storage of oligosaccharides, which may indicate the presence of one of the infantile Pompe disease, α-mannosidosis, Gm1-gangliosidosis, Sandhoff disease, sialidosis, galactosialidosis, I-cell disease, and aspartylglucosaminuria.

Analysis of urinary oligosaccharides in lysosomal storage disorders by capillary high-performance anion-exchange chromatography-mass spectrometry

Many lysosomal storage diseases are characterized by an increased urinary excretion of glycoconjugates and oligosaccharides that are characteristic for the underlying enzymatic defect. Here, we have used capillary high-performance anion-exchange chromatography (HPAEC) hyphenated to mass spectrometry to analyze free oligosaccharides from urine samples of patients suffering from the lysosomal storage disorders fucosidosis, α-mannosidosis, G(M1)-gangliosidosis, G(M2)-gangliosidosis, and sialidosis. Glycan fingerprints were registered, and the patterns of accumulated oligosaccharides were found to reflect the specific blockages of the catabolic pathway. Our analytical approach allowed structural analysis of the excreted oligosaccharides and revealed several previously unpublished oligosaccharides. In conclusion, using online coupling of HPAEC with mass spectrometric detection, our study provides characteristic urinary oligosaccharide fingerprints with diagnostic potential for lysosomal storage disorders.

Towards a selected reaction monitoring mass spectrometry fingerprint approach for the screening of oligosaccharidoses

The oligosaccharidoses are a group of metabolic disorders resulting from a deficiency in enzymes responsible for the catabolism of protein bound oligosaccharides and are typified by the accumulation of corresponding sugars in the urine. Screening is typically accomplished using thin layer chromatography. However, analyte specificity can be a problem and thus complicate interpretation of results. For this reason we developed a mixed mode liquid chromatography tandem mass spectrometry assay for the screening of the oligosaccharidoses which potentially mitigates many of the problems associated with thin layer chromatography. Samples from patients previously diagnosed with I-Cell disease, mannosidosis, Pompe, galactosialidosis, and fucosidosis were derivatized with 3-methyl-1-phenyl-2-pyrazolin-5-one and subjected to analysis by liquid chromatography tandem mass spectrometry. Results were compared to normal control samples. Preliminary results suggest that each oligosaccharidoses produces a unique selected reaction monitoring fingerprint and that the developed method may be an effective screening and diagnostic tool for these disorders.

Glycan profiling of urine, amniotic fluid and ascitic fluid from galactosialidosis patients reveals novel oligosaccharides with reducing end hexose and aldohexonic acid residues

Urine, amniotic fluid and ascitic fluid samples of galactosialidosis patients were analyzed and structurally characterized for free oligosaccharides using capillary high-performance anion-exchange chromatography with pulsed amperometric detection and online mass spectrometry. In addition to the expected endo-beta-N-acetylglucosaminidase-cleaved products of complex-type sialylated N-glycans, O-sulfated oligosaccharide moieties were detected. Moreover, novel carbohydrate moieties with reducing-end hexose residues were detected. On the basis of structural features such as a hexose-N-acetylhexosamine-hexose-hexose consensus sequence and di-sialic acid units, these oligosaccharides are thought to represent, at least in part, glycan moieties of glycosphingolipids. In addition, C(1)-oxidized, aldohexonic acid-containing versions of most of these oligosaccharides were observed. These observations suggest an alternative catabolism of glycosphingolipids in galactosialidosis patients: oligosaccharide moieties from glycosphingolipids would be released by a hitherto unknown ceramide glycanase activity. The results show the potential and versatility of the analytical approach for structural characterization of oligosaccharides in various body fluids.

A longitudinal study of Taiwanese sialidosis type 1: an insight into the concept of cherry-red spot myoclonus syndrome

BACKGROUND AND PURPOSE

Sialidosis type 1 (ST-1) is a neurodegenerative disorder with limited long-term follow-up report. This study is to document the chronological profile of ST-1.

METHODS

We perform serial analysis of 17 Taiwanese patients with ST-1 focusing on evolution of clinical features, electrophysiological findings, genetic studies, and neuroimage examinations.

RESULTS

All patients had a mutation at 554A-->G in exon 3 of the NEU1 gene causing Ser182Gly substitution. Fifteen patients were homozygous. Two patients were heterozygous with novel mutations, 956C-->T causing Ala319Val in one and 163C-->T causing Gln55stop codon in the other. The neuraminidase activity was markedly decreased in all 11 available patients. Only three patients (17.6%) manifested the macular cherry-red spot. The majority of patients (82.3%) developed full-blown manifestation of myoclonus, ataxia, and seizures within 5 years. Abnormal somatosensory evoked potentials with giant cortical waves were found in all patients. Prolonged P100 peak latency of the visual evoked potentials (VEPs) were found in 16 patients (94.1%) in the early stage even without visual symptoms.

CONCLUSION

ST-1 in Taiwanese population illustrates distinct characteristics of phenotype with infrequent cherry-red spot. We suggest to screen the NEU1 mutations in patients presenting action myoclonus with abnormal VEPs, even without macular cherry-red spots.

Lipidomics in diagnosis of lipidoses

A review is presented of the major clinical features of a number of glycolipidoses including Fabry, Gaucher, Tay-Sachs, metachromatic leukodystrophy as well as CeroidLipofucinosis and Sjogren-Larsson syndrome. The possibilities offered by lipidomics for diagnosis and follow-up after enzyme replacement therapy are presented from a practical perspective. The contribution of HPLC coupled with tandem mass spectrometry has considerably simplified the detection and assay of abnormal metabolites. Corresponding internal standards consisting of weighed mixtures of the stable-isotope labeled metabolites required to calibrate and quantitate lipid components of these orphan diseases standards have yet to become commercially available. A lipidomics approach has been found to compare favorably with DNA-sequence analysis for the rapid diagnosis of pre-birth syndromes resulting from these multiple gene defects. The method also seems to be suitable for screening applications in terms of a high throughput combined with a low rate of false diagnoses based on the wide differences in metabolite concentrations found in affected patients as compared with normal subjects. The practical advantages of handling samples for lipidomic diagnoses as compared to enzyme assay are presented for application to diagnosis during pregnancy.

A mass spectrometric strategy for profiling glycoproteinoses, Pompe disease, and sialic acid storage diseases

Glycoproteinoses, Pompe disease, and sialic acid storage diseases are characterized by a massive accumulation of unprocessed oligosaccharides and/or glycoconjugates in urine. The identification of these glycocompounds is essential for a proper diagnosis. In this study, we investigated the potential of MALDI-TOF-MS to identify glycocompounds present in urine from patients with different inborn errors of glycan metabolism. Urinary glycocompounds were permethylated, and analyzed using GC-MS and MALDI-TOF-MS. In order to confirm tentative assignments, a second aliquot of urine was purified on a C18 Sep-Pak cartridge and glycocompounds were desalted on a column of nonporous graphitized carbon. The glycocompounds were then sequentially on-plate digested using an array of exoglycosidases. A range of disease-specific oligosaccharides as well as glycopeptides was identified for all oligosacchariduria models. In addition, free sialic acid accumulated in urine from a patient suffering from French-type sialuria, has been detected by a GC-MS approach, which could be applied to other sialic acid storage diseases. This procedure is simple, and can be performed in few simple steps in less than 24 h. This current method can be applied for newborn screening for other inherited metabolic diseases as well as for assessing treatments in clinical trials.