Isolation and characterization of major urinary amino acid O-glycosides and a dipeptide O-glycoside from a new lysosomal storage disorder (Kanzaki disease). Excessive excretion of serine- and threonine-linked glycan in the patient urine

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

GH101 family of glycoside hydrolases: subfamily structure and evolutionary connections with other families

The GH101 family is composed of endo-alpha-N-acetylgalactosaminidases and their homologues. Pairwise sequence comparison and phylogenetic analysis allowed us to distinguish five to six subfamilies in this family. Diverse domain structures were found among the family members. Usually they have five irreplaceable and some optional domains. Iterative screening of the protein database revealed an evolutionary relationship of the GH101 catalytic domain with glycoside hydrolase domains from GH13, GH31, and GH70 families. Among other homologous proteins we have found representatives of COG1649, as well as members of four new families of predicted glycoside hydrolases (GHL1-GHL4).

Identification of Monosialylated N-glycoforms in the CDG Urinome by Ion Mobility Tandem Mass Spectrometry: The Potential for Clinical Applications

Introduction

A novel approach of ion mobility tandem mass spectrometry (IMS-MS/MS) is applied to analysis of human glycourinome to obtain carbohydrate pattern data of congenital disorders of glycosylation patient. Overlapping of the complex carbohydrate mass range landscape has been highly reduced upon IMS-MS procedure, allowing more efficient identification by mapping and sequencing of glycan precursor ions, following their separation by mobility, according to difference in drift time through the traveling wave IMS cell. Intact and truncated N- and O-glycan structures modified by sialylation and fucosylation were identified according to their drift time separated molecular ions and submitted to fragmentation in a narrow mass window.

IMS CID MS/MS Analysis

The fragmentation spectra generated from the IMS separated precursor ions contain series of fragment ions maintaining the same mobility as their parent ions, and the assignment accuracy can be significantly enhanced.

Conclusion

According to the specific fragment ion patterns, carbohydrate epitopes described to be involved in pathological processes were assigned. A high potential of this glycomics-based strategy for clinical applications can be presented.

Identification of glycoconjugates in the urine of a patient with congenital disorder of glycosylation by high-resolution mass spectrometry

More than 150 molecular species were detected in a single glycoconjugate fraction obtained from urine of a congenital disorders of glycosylation (CDG) patient by use of high-resolution FT-ICR MS. With respect to its high-mass accuracy and resolving power, FT-ICR MS represents an ideal tool for analysis of single components in complex glycoconjugate mixtures obtained from body fluids. The presence of overlapping nearly isobaric ionic species in glycoconjugate mixtures obtained from CDG patient's urine was postulated from fragmentation data of several precursor ions obtained by nanoESI Q-TOF CID. Their existence was confirmed by high-resolution/high-mass accuracy FT-ICR MS detection. High-resolution FT-ICR mass spectra can, therefore, be generally considered for glycoscreening of complex mixture samples in a single stage. From the accurate molecular ion mass determinations the composition of glycoconjugate species can be identified. Particular enhancement of identification is offered by computer-assisted calculations in combination with monosaccharide building block analysis, which can be extended by considerations of non-carbohydrate modifications, such as amino acids, phosphates and sulfates. Taking advantage of this strategy, the number of compositions assigned to mass peaks was significantly increased in a fraction obtained from urine by size exclusion and anion exchange chromatography.

Blood group A glycosphingolipid accumulation in the hair of patients with α-N-acetylgalactosaminidase deficiency

In the hair of individuals with blood group AB, the level of blood group A glycosphingolipids is much lower than that of blood group B. We hypothesized that in hair, blood group A determinants are converted by alpha-N-acetylgalactosaminidase (alpha-NAGA, E.C.3.2.1.49) to H determinants. To address our hypothesis, the relative amount of ABH glycosphingolipids in hairs and nails of normal subjects, patients with Kanzaki disease, and heterozygous carriers of alpha-NAGA deficiency were analyzed by dot-blotting and enzyme-linked immunosorbent assay. In hair from normal subjects with blood group B, ABH glycosphingolipids consisted of 88% blood group B- and 12% blood group H glycosphingolipids. In blood group A subjects, 14% were group A- and 86% were group H glycosphingolipids. In Kanzaki patients, 81% were blood group A- and 19% were blood group H glycosphingolipids. In 2 alpha-NAGA deficiency carriers, the ABH glycosphingolipids consisted of 67% blood group A- and 33% blood group H glycosphingolipids. These results indicate that blood group A glycosphingolipids are catabolized to H glycosphingolipids by alpha-NAGA, resulting in lower levels of blood group A glycosphingolipids in the hair of normal subjects, and alpha-NAGA deficiency causes accumulation of blood group A glycosphingolipids in the hair of Kanzaki patients. This finding is of clinical relevance because it suggests that hair may be used to diagnose and assess the alpha-NAGA status of individuals.

One-Pot Synthesis of Sialo-Containing Glycosyl Amino Acids by Use of anN-Trichloroethoxycarbonyl-?-thiophenyl Sialoside

We describe an efficient synthesis of 2,6- and 2,3-sialyl T antigens linked to serine in a one-pot glycosylation. We first investigated the glycosidation of thiosialosides by varying the N-protecting group. Modification of the C-5 amino group of beta-thiosialosides into the N-9-fluorenylmethoxycarbonyl, N-2,2,2-trichloroethoxycarbonyl (N-Troc), and N-trichloroacetyl derivatives enhanced the reactivity of these compounds towards glycosidation. Addition of a minimum amount of 3 A molecular sieves was also effective in improving the yield of alpha-linked sialosides. Next, we conducted one-pot syntheses of the glycosyl amino acids by using the N-Troc sialyl donor. The N-Troc derivative can be converted into the N-acetyl derivative without racemization of the amino acids. Branched-type one-pot glycosylation, initiated by regioselective glycosylation of the 3,6-dihydroxy galactoside with the N-Troc-beta-thiophenyl sialoside, provided the protected 2,6-sialyl T antigen in good yield. Linear-type one-pot glycosylation, initiated by chemoselective glycosylation of galactosyl fluoride with the N-Troc-beta-thiophenyl sialoside, afforded the protected 2,3-sialyl T antigen in excellent yield. Both protected glycosyl amino acids were converted into the fully deprotected 2,6- and 2,3-sialyl T antigens linked to serine in good yields.

Three dimensional structural studies of alpha-N-acetylgalactosaminidase (alpha-NAGA) in alpha-NAGA deficiency (Kanzaki disease): different gene mutations cause peculiar structural changes in alpha-NAGAs resulting in different substrate specificities and clinical phenotypes

BACKGROUND

Kanzaki disease (OMIM#104170) is attributable to a deficiency in alpha-N-acetylgalactosaminidase (alpha-NAGA; E.C.3.2.1.49), which hydrolyzes GalNAcalpha1-O-Ser/Thr. Missense mutations, R329W or R329Q were identified in two Japanese Kanzaki patients. Although they are on the same codon, the clinical manifestation was more severe in R329W because an amino acid substitution led to protein instability resulting in structural change, which is greater in R329W than in R329Q.

OBJECTIVE

To examine whether the different clinical phenotypes are attributable to the two mutations.

METHODS

Plasma alpha-NAGA activity and urinary excreted glycopeptides were measured and three-dimensional models of human alpha-NAGA and its complexes with GalNAcalpha1-O-Ser and GalNAcalpha1-O-Thr were constructed by homology modeling.

RESULTS

Residual enzyme activity was significantly higher in the R329Q- than the R329W mutant (0.022+/-0.005 versus 0.005+/-0.001 nmol/h/ml: p<0.05); the urinary ratios of GalNAcalpha1-O-Ser:GalNAcalpha1-O-Thr were 2:10 and 8:10, respectively. GalNAcalpha1-O-Ser/Thr fit tightly in a narrow space of the active site pocket of alpha-NAGA. GalNAcalpha1-O-Thr requires a larger space to associate with alpha-NAGA because of the side chain (CH3) of the threonine residue.

CONCLUSION

Our findings suggest that the association of alpha-NAGA with its substrates is strongly affected by the amino acid substitution at R329 and that the association with GalNAcalpha1-O-Thr is more highly susceptible to structural changes. The residual mutant enzyme in R329W could not associate with GalNAcalpha1-O-Thr and GalNAcalpha1-O-Ser. However, the residual mutant enzyme in R329Q catalyzed GalNAcalpha1-O-Ser to some extent. Therefore, the urinary ratio of GalNAcalpha1-O-Ser:GalNAcalpha1-O-Thr was lower and the clinical phenotype was milder in the R329Q mutation. Structural analysis revealed biochemical and phenotypic differences in these Kanzaki patients with the R329Q and R329W mutation.

Neurologic manifestations of Kanzaki disease

We describe the neurologic findings in a patient with alpha-N-acetylgalactosaminidase deficiency (Kanzaki disease). Clinical and electrophysiologic studies revealed sensory-motor polyneuropathy, and sural nerve pathology showed decreased density of myelinated fibers with axonal degeneration. The patient had mildly impaired intellectual function with abnormal brain MRI and sensory-neuronal hearing impairment with repeated episodes of vertigo attacks. These findings suggest that Kanzaki disease may develop neurologic complications in the CNS and peripheral nervous system.

A thin chip microsprayer system coupled to Fourier transform ion cyclotron resonance mass spectrometry for glycopeptide screening

A thin polymer microchip was coupled with a Fourier transform ion cyclotron resonance (FTICR) 9.4 T mass spectrometer and the method was optimized in negative ion mode for glycopeptide screening. The interface between the polymer microchip and FTICR mass spectrometer consists of an in-laboratory conceived and designed mounting system that exhibits robust and controllable alignment of the chip toward the inlet of the mass spectrometer. The particular attribute of the polymer chip coupled to the FTICR mass spectrometer, to achieve an increase in ionization efficiency and sensitivity under the premise of high mass accuracy of detection, is highlighted by the large number of major and minor glycopeptide structures detected and identified in highly heterogeneous mixtures obtained from urine matrices. Glycoforms expressing various saccharide chain lengths ranging from tri- to dodecasaccharide, bearing up to three sialic acid moieties, could be detected and assigned based on the accuracy of the mass measurement (average mass deviation below 6 ppm) of their molecular ions. -Thin chipESI-FTICRMS is a potent novel system for glycomic screening of complex mixtures, as demonstrated for identification of singly sialylated O-glycosylated amino acids and peptides from urine matrices, and could be considered for general applicability in the glycoanalytical field.

Structural and immunocytochemical studies on alpha-N-acetylgalactosaminidase deficiency (Schindler/Kanzaki disease)

Alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency (Schindler/Kanzaki disease) is a clinically and pathologically heterogeneous genetic disease with a wide spectrum including an early onset neuroaxonal dystrophy (Schindler disease) and late onset angiokeratoma corporis diffusum (Kanzaki disease). In alpha-NAGA deficiency, there are discrepancies between the genotype and phenotype, and also between urinary excretion products (sialyl glycoconjugates) and a theoretical accumulated material (Tn-antigen; Gal NAcalpha1-O-Ser/Thr) resulting from a defect in alpha-NAGA. As for the former issue, previously reported genetic, biochemical and pathological data raise the question whether or not E325K mutation found in Schindler disease patients really leads to the severe phenotype of alpha-NAGA deficiency. The latter issue leads to the question of whether alpha-NAGA deficiency is associated with the basic pathogenesis of this disease. To clarify the pathogenesis of this disease, we performed structural and immunocytochemical studies. The structure of human alpha-NAGA deduced on homology modeling is composed of two domains, domain I, including the active site, and domain II. R329W/Q, identified in patients with Kanzaki disease have been deduced to cause drastic changes at the interface between domains I and II. The structural change caused by E325K found in patients with Schindler disease is localized on the N-terminal side of the tenth beta-strand in domain II and is smaller than those caused by R329W/Q. Immunocytochemical analysis revealed that the main lysosomal accumulated material in cultured fibroblasts from patients with Kanzaki disease is Tn-antigen. These data suggest that a prototype of alpha-NAGA deficiency in Kanzaki disease and factors other than the defect of alpha-NAGA may contribute to severe neurological disorders, and Kanzaki disease is thought to be caused by a single enzyme deficiency.

Morphological and biochemical studies of human beta-mannosidosis: identification of a novel beta-mannosidase gene mutation

BACKGROUND

There are seven well-known lysosomal storage diseases that produce angiokeratoma corporis diffusum clinically. beta-Mannosidosis (MANB1; OMIM248510), first reported in humans in 1986, is a rare hereditary lysosomal storage disease caused by a deficiency of the enzyme beta-mannosidase. Since then, 13 cases of beta-mannosidase deficiency in ten families have been described. A human beta-mannosidase mutation has been reported only by Alkhayat et al. in 1998.

OBJECTIVES

To clarify its pathogenesis we did electron microscopic, biochemical and molecular biological investigations of a Japanese patient with beta-mannosidosis.

METHODS

Ultrastructural analyses, enzyme assays, cell culture and mRNA and genomic DNA were sequenced to find mutations in the beta-mannosidase gene.

RESULTS

Electron microscopy of skin biopsy specimens from the patient showed cytoplasmic vacuolation of lysosomes in blood and lymph vessels, endothelial cells, fibroblasts, secretory portions of eccrine sweat glands, neural cells and basal keratinocytes in the epidermis. This vacuolation was also observed in cultured keratinocytes and fibroblasts. Assays of seven enzyme activities in plasma and cultured skin fibroblasts showed a marked decrease of beta-mannosidase activity. Sequencing the beta-mannosidase cDNA revealed a four-base (ATAA) insertion between exons 7 and 8, resulting in a frameshift at codon 321 and termination at codon 325. Analysis of the patient's genomic DNA revealed a novel homozygous A(+1)-->G splice site mutation in intron 7.

CONCLUSIONS

To our knowledge, this is the first case of beta-mannosidosis reported in Japan and the second report in which a gene mutation is identified. The biological importance of beta-mannose moieties in glycoproteins in basal keratinocytes is suggested.

Molecular cloning of cDNA encoding alpha-N-acetylgalactosaminidase from Acremonium sp. and its expression in yeast

Alpha-N-acetylgalactosaminidase (alpha-GalNAc-ase; EC 3.2.1.49) is an exoglycosidase specific for the hydrolysis of terminal alpha-linked N-acetylgalactosamine in various sugar chains. The cDNA, nagA, encoding alpha-GalNAc-ase from Acremonium sp. was cloned, sequenced, and expressed in yeast Saccharomyces cerevisiae. The nagA contains an open reading frame which encodes for 547 amino acid residues including 21 residues of a signal peptide in its N-terminal. The calculated molecular mass of mature protein from the deduced amino acid sequence of nagA is 57260 Da, which corresponds to the value obtained from SDS-PAGE of native and recombinant enzymes treated with endo-beta-N-acetylglucosaminidase H. The amino acid sequence of NagA showed significant similarity to those of eukaryotic alpha-GalNAc-ases and alpha-galactosidases (alpha-Gal-ases), particularly alpha-Gal-ase A (AglA) from Aspergillus niger. Phylogenetic analysis revealed that NagA does not belong to the cluster of vertebrate alpha-GalNAc-ase and alpha-Gal-ase but forms another cluster with AglA and yeast alpha-Gal-ases. Thus, the evolutionary origin of the fungal alpha-GalNAc-ase is suggested to be different from that of vertebrate alpha-GalNAc-ase. This is the first report of a microbial alpha-GalNAc-ase gene.

A new case of alpha-N-acetylgalactosaminidase deficiency with angiokeratoma corporis diffusum, with Ménière's syndrome and without mental retardation

alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency is a rare hereditary lysosomal storage disease, and only three alpha-NAGA-deficient patients with angiokeratoma corporis diffusum (Kanzaki) have been described. We report a further case in a 47-year-old Japanese woman, the product of a consanguineous marriage. The remarkable findings in this patient were her normal intelligence, Ménière's syndrome, disturbance of peripheral sensory nerves, hearing loss and cardiac hypertrophy. alpha-NAGA enzyme activity in her plasma was 0.77% of the normal value. Other enzyme activities, such as alpha-galactosidase, beta-galactosidase, alpha-L-fucosidase, beta-mannosidase and aspartylglucosaminidase, were within normal limits. A large quantity of amino acid O-glycans was detected in her urine. Gene analysis revealed a novel point mutation (G-->A transition) at nucleotide 11018 (986 in the cDNA) resulting in an Arg-329-Gln substitution. Kanzaki disease has the same enzyme defect as Schindler disease, but the manifestations are quite different.

Human alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency: no association with neuroaxonal dystrophy?

Two new individuals with alpha-NAGA deficiency are presented. The index patient, 3 years old, has congenital cataract, slight motor retardation and secondary demyelinisation. Screening of his sibs revealed an alpha-NAGA deficiency in his 7-year-old healthy brother who had no clinical or neurological symptoms. Both sibs are homozygous for the E325K mutation, the same genotype that was found in the most severe form of alpha-NAGA deficiency presenting as infantile neuroaxonal dystrophy. Thus, at the age of 7 years the same genotype of alpha-NAGA may present as a 'non-disease' (present healthy case) and can be associated with the vegetative state (the first two patients described with alpha-NAGA deficiency). The clinical heterogeneity among the 11 known individuals with alpha-NAGA deficiency is extreme, with a 'non-disease' (two cases) and infantile neuroaxonal dystrophy (two cases) at the opposite sides of the clinical spectrum. The broad spectrum is completed by a very heterogeneous group of patients with various degrees of epilepsy/behavioural difficulties/psychomotor retardation (four patients) and a mild phenotype in adults without overt neurological manifestations who have angiokeratoma and clear vacuolisation in various cell types (three cases). These observations are difficult to reconcile with a straightforward genotype-phenotype correlation and suggest that factors or genes other than alpha-NAGA contribute to the clinical heterogeneity of the 11 patients with alpha-NAGA deficiency.

Human alpha-N-acetylgalactosaminidase: site occupancy and structure of N-linked oligosaccharides

Human alpha-N-acetylgalactosaminidase (alpha-GalNAc; also known as alpha-galactosidase B) is the lysosomal exoglycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties in glycoconjugates. Mutagenesis studies indicated that the first five (N124, N177, N201, N359, and N385) of the six potential N-glycosylation sites were occupied. Site 3 occupancy was important for enzyme function and stability. Characterization of the N-linked oligosaccharide structures on the secreted enzyme overexpressed in Chinese hamster ovary cells revealed highly heterogeneous structures consisting of complex (approximately 53%), hybrid (approximately 12%), and high mannose-type (approximately 33%) oligosaccharides. The complex structures were mono-, bi-, 2,4-tri-, 2,6-tri-, and tetraantennary, among which the biantennary structures were most predominant (approximately 53%). Approximately 80% of the complex oligo-saccharides had a core-region fucose and 50% of the complex oligosaccharides were sialylated exclusively with alpha-2,3-linked sialic acid residues. The majority of hybrid type oligo-saccharides were GalGlcNAcMan(6)GlcNAc-Fuc(0-1)GlcNAc. Approximately 54% of the hybrid oligosaccharide were phosphorylated and one-third of these structures were further sialylated, the latter representing unique phosphorylated and sialylated structures. Of the high mannose oligosaccharides, Man(5-7)GlcNAc(2) were the predominant species (approximately 90%) and about 50% of the high mannose oligosaccharides were phosphorylated, exclusively as monoesters whose positions were determined. Comparison of the oligosaccharide structures of alpha-GalNAc and alpha-galactosidase A, an evolutionary-related and highly homologous exoglycosidase, indicated that alpha-GalNAc had more completed complex chains, presumably due to differences in enzyme structure/domains, rate of biosynthesis, and/or aggregation of the overexpressed recombinant enzymes.

Human alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency: new mutations and the paradox between genotype and phenotype

Up to now eight patients with alpha-NAGA deficiency have been described. This includes the newly identified patient reported here who died unexpectedly aged 1 1/2 years of hypoxia during convulsions; necropsy was not performed. Three patients have been genotyped previously and here we report the mutations in the other five patients, including two new mutations (S160C and E193X). The newly identified patient is consanguineous with the first patients reported with alpha-NAGA deficiency and neuroaxonal dystrophy and they all had the alpha-NAGA genotype E325K/E325K. Clinical heterogeneity among patients with alpha-NAGA deficiency is extreme. Two affected sibs, homozygotes for E325K, are severely affected and have the signs and symptoms of infantile neuroaxonal dystrophy, but prominent vacuolisation is lacking. The mildly affected patients (two families, three patients) at the opposite end of the clinical spectrum have clear vacuolisation and angiokeratoma but no overt neurological manifestations. Two of them are homozygous for the stop mutation E193X, leading to complete loss of alpha-NAGA protein. These observations are difficult to reconcile with a simple genotype-phenotype correlation and we suggest that factors or genes other than alpha-NAGA contribute to the clinical heterogeneity of the eight patients with alpha-NAGA deficiency. At the metabolic level, the patients with alpha-NAGA deficiency are similar. The major abnormal urinary oligosaccharides are sialylglycopeptides of the O linked type. Our enzymatic studies indicated that these compounds are not the primary lysosomal storage products.

Characterization of four monosialo and a novel disialo Asn N-glycosides from the urine of a patient with aspartylglycosaminuria

We previously reported for the first time two Japanese patients with aspartylglycosaminuria (AGU). A novel disialo Asn N-glycoside (AG-5) has been isolated from the urine of one of the patients in addition to four known monosialo Asn N-glycosides (AG-1 to AG-4) by gel filtration and anion exchange chromatography in this study. Final purification of AG-5 was achieved by an electrochemical chromatographic method, high performance liquid chromatography with pulsed amperometric detector (HPLC-PAD). The yield of AG-5 was approximately 1 mg l-1 urine. The chemical structures of AG-1 to AG-5 were characterized by gas-liquid chromatography, a permethylation study, fast atom bombardment-mass spectrometry (FAB-MS), and nuclear magnetic resonance (NMR). Based on the structural analysis, AG-5 had the following novel structure: NeuAc alpha 2-->8NeuAc alpha 2-->3Gal beta 1-->4GlcNAc beta 1-->Asn.

Histopathologic and ultrastructural studies of angiokeratoma corporis diffusum in Kanzaki disease

A novel metabolic disease, angiokeratoma corporis diffusum (Kanzaki), was the subject of an extensive histopathologic and ultrastructural study. Findings included dilated lymph and blood vessels in the upper dermis with an orthokeratortic, thickened, horny layer in well developed angiokeratoma. In the early papules, a few sporadic dyskeratotic keratinocytes were present in the epidermis with or without a thickened horny layer. Vesicular clear vacuolation was clearly observed in the cytoplasm of the secretory portion of the eccrine sweat glands, but none was observed in the vascular endothelial cells with hematoxylin-eosin staining. Using electron microscopy, lysosomal vacuolation was observed in many cell types, including eccrine sweat gland cells, vascular endothelial cells, dermal fibroblasts, dermal neural cells, lymphocytes of peripheral blood in the skin, and glomerular endothelial cells, but none was noted in the epithelial cells of the kidney. Widely dilated vacuoles were found to contain only a small amount of fuzzy filamentous material in the vascular endothelial cells, filamentous or electron-dense granular substances in fibroblasts, and electron-dense, lamellated or homogeneous structures in eccrine sweat gland cells and in neural cells. Ultracytochemical examination revealed glycoconjugates in dilated lysosomes. Characteristics of Kanzaki Disease were shown to differ from those of Fabry disease or any other lysosomal storage disease.

alpha-N-acetylgalactosaminidase deficiency with mild clinical manifestations and difficult biochemical diagnosis

Two additional patients with alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency are described. An 11-month-old girl with nonconsanguineous parents had generalized seizures and no angiokeratoma. Biochemical investigation showed persistent slight oligosacchariduria; enzymatic analysis of plasma, leukocytes, and fibroblasts revealed profound alpha-NAGA deficiency. Heterozygote enzyme levels were found in both parents. The mother has epilepsy, and epilepsy is present in the father's family. A younger, clinically healthy brother also had the enzyme deficiency. Electron microscopy of lymphocytes from the index patient showed no vacuolization. Incubation of cultured fibroblasts with Helix pomatia lectin showed the presence of intracellular N-acetylgalactosamine-containing storage material, not present in a series of 12 normal fibroblast lines. Our cases cannot be classified definitely as infantile cases. Biochemically the diagnosis could easily have been missed. Urinary oligosaccharide pattern after resorcinol staining was identical to those previously described, but excretion was significantly lower than in the reported infantile cases and the bands disappeared after the urine was desalted. The enzyme defect in leukocytes would have been missed with one of the commercial substrates used. For this mild variant of alpha-NAGA deficiency, the clinical pattern is not yet clear; a longer follow-up period is needed.

Measurement of sialic acid in serum and urine: clinical applications and limitations

Many recent studies have examined the sialic acid content of serum or urine in various pathological states. We have briefly reviewed the substances which contribute to the observed total sialic acid concentration, and given an overview of assay methods used. Three major areas of clinical interest in sialic acid metabolism are discussed. Serum total sialic acid, 'lipid-bound' and 'protein bound' sialic acid have all been proposed as tumour markers; but the usefulness of any of these tests is severely limited by changes due to accompanying inflammatory processes. Serum total sialic acid is not a valuable simple marker of an acute phase response. Urinary free and bound sialic acid measurements should be included in screening protocols for inherited disorders of lysosomal metabolism. Current developments in research and potential applications within the clinical biochemistry laboratory are briefly discussed.

Two Japanese cases with aspartylglycosaminuria: clinical and morphological features

Two members of a consanguineous Japanese family with a clinical picture of aspartylglycosaminuria (AGU) are described. Both patients exhibited mental retardation, coarse facial features, angiokeratoma and myoclonic seizures. Biochemical studies showed elevated excretion of urinary sialyloligosaccharides and decreased activity of aspartylglycosaminidase in lymphoblasts. Morphologic studies of skin biopsy specimens showed many clear vacuoles mainly in the vascular endothelial cells and secretory cells of the sweat glands. Osmiophilic lamellar cytoplasmic inclusions were also noted in the ganglion cells in rectal biopsy. The ethnic distribution of AGU may be more widespread than previously suspected and appears not to be restricted to Finnish populations. Ours are the first Japanese patients diagnosed as AGU. We conclude that AGU should also be included in the differential diagnosis of mentally retarded patients in Asian countries.

Biosynthesis of human alpha-N-acetylgalactosaminidase: defective phosphorylation and maturation in infantile alpha-NAGA deficiency

The biosynthesis of human alpha-N-acetylgalactosaminidase (alpha-NAGA) was studied in normal fibroblasts and in cells from patients with infantile alpha-NAGA deficiency. Normal alpha-NAGA is synthesized as a 52 kDa precursor which matures to a 49 kDa species through phosphorylation and carbohydrate triming. Fibroblasts from the patients synthesize normal amounts of a 52 kDa precursor, however phosphorylation does not occur and this precursor is subsequently degraded intracellularly.

A method for the rapid detection of urinary glycopeptides in alpha-N-acetylgalactosaminidase deficiency and other lysosomal storage diseases

A new method is described for the detection of abnormal urinary oligosaccharide and glycopeptide excretion by thin layer chromatography and differential visualization of oligosaccharides and glycopeptides. This method permits rapid screening and identification of disorders characterized by oligosacchariduria and glycopeptiduria including alpha-N-acetylgalactosaminidase deficiency, angiokeratoma corporis diffusum with glycopeptiduria, aspartylglucosaminuria, galactosialidosis, fucosidosis, GM1 gangliosidosis and sialidoses 1 and 2. Of note, the characterization of the glycopeptide excretion profiles in patients with alpha-N-acetylgalactosaminidase deficiency and angiokeratoma corporis diffusum with glycopeptiduria revealed essentially identical patterns, indicating the metabolic relatedness of these two phenotypically distinct conditions. Use of this improved thin layer chromatographic method should enhance routine screening of patients for lysosomal storage diseases as well as permit the identification of new disorders resulting from defective oligosaccharide and/or glycoprotein metabolism.

Molecular cloning of two species of cDNAs for human alpha-N-acetylgalactosaminidase and expression in mammalian cells

Two species of cDNAs for human alpha-N-acetylgalactosaminidase were isolated from a human fibroblast cDNA library. The two species differ each other by a 70 bp insertion in the coding region. Transient expression study in COS cells demonstrated that only the cDNA without the 70 bp insertion expressed alpha-N-acetylgalactosaminidase activity. Analysis of mRNA species utilizing polymerase chain reaction revealed that the majority of the mRNA does not contain the 70 bp insertion, and the mRNA containing the 70 bp insertion is present only in a minor amount in human brain.

Action of endo-alpha-N-acetylgalactosaminidase from Alcaligenes sp. on amino acid-O-glycans: comparison with the enzyme from Diplococcus pneumoniae

Endo-alpha-N-acetylgalactosaminidase from Alcaligenes sp. released the disaccharide, Gal beta 1----3GalNAc, from both dansylated serine-GalNAc-Gal and threonine-GalNAc-Gal, and showed higher activity on the former than the latter. The Km values were 0.17 mM and 1.43 mM with DNS-Ser-GalNAc-Gal and DNS-Thr-GalNAc-Gal, respectively. The optimum pHs were found to be 4.5-7.5 and 4.5-6.0 on DNS-Ser-GalNAc-Gal and DNS-Thr-GalNAc-Gal, respectively. On the contrary, the enzyme from Diplococcus pneumoniae had low activity to release the disaccharide from the amino acid-O-glycans. The possibility that the same O-glycoside but linked to different aglycon amino acids may play a different biological role in glycoproteins is discussed.