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

Chemo-Enzymatic Production of 4-Nitrophenyl-2-acetamido-2-deoxy-α-D-galactopyranoside Using Immobilized β-N-Acetylhexosaminidase

α-Nitrophenyl derivatives of glycosides are convenient substrates used to detect and characterize α-N-acetylgalactosaminidase. A new procedure combining chemical and biocatalytic steps was developed to prepare 4-nitrophenyl-2-acetamido-2-deoxy-α-D-galactopyranoside (4NP-α-GalNAc). The α-anomer was prepared through chemical synthesis of an anomeric mixture followed by selective removal of the β-anomer using specific enzymatic hydrolysis. Fungal β-N-acetylhexosaminidase (Hex) from Penicillium oxalicum CCF 1959 served this purpose owing to its high chemo-and regioselectivity towards the β-anomeric N-acetylgalactosamine (GalNAc) derivative. The kinetic measurements of the hydrolytic reaction showed that the enzyme was not inhibited by the substrate or reaction products. The immobilization of Hex in lens-shaped polyvinyl alcohol hydrogel capsules provided a biocatalyst with very good storage and operational stability. The immobilized Hex retained 97% of the initial activity after ten repeated uses and 90% of the initial activity after 18 months of storage at 4 °C. Immobilization inactivated 65% of the enzyme activity. However, the effectiveness factor and kinetic and mass transfer phenomena approached unity indicating negligible mass transfer limitations.

Multiple exo-glycosidases in human serum as detected with the substrate DNP-α-GalNAc. I. A new assay for lysosomal α-N-acetylgalactosaminidase

This paper presents a new assay to determine the activity of the lysosomal enzyme α-N-acetylgalactosaminidase (Naga, EC 3.2.1.49) in human serum. It is based on the use of a new chromogenic substrate, DNP-α-GalNAc (2,4-dinitrophenyl-N-acetyl-α-D-galactosaminide) and is performed at pH 4.3 and 37 °C. This allows continuous monitoring of the absorbance of the released DNP. The assay can be performed with a standard spectrophotometer. Compared to established methods using an endpoint assay with MU-α-GalNAc (4-methylumbelliferyl-GalNAc), the present method gives a ca. 3-fold higher specific activity, while only one tenth of the serum concentration in the assay is required. Hence, the assay is at least 30-fold more sensitive than that with MU-α-GalNAc. The pH dependence of the reaction with DNP-α-GalNAc in the pH 3.5 to 6.5 region, while using 4% serum in the assay, shows only one peak around pH 4. This pH optimum is similar to that reported with MU-α-GalNAc. In the accompanying paper (S.P.J Albracht and J. Van Pelt (2017) Multiple exo-glycosidases in human serum as detected with the substrate DNP-α-GalNAc. II. Three α-N-acetylgalactosaminidase-like activities in the pH 5 to 8 region. BBA Clin. 8 (2017) 90-96), the method is used to show that, under special assay conditions, three more Naga-like activities can be uncovered in human serum.

Lysosomal storage diseases

Lysosomes are cytoplasmic organelles that contain a variety of different hydrolases. A genetic deficiency in the enzymatic activity of one of these hydrolases will lead to the accumulation of the material meant for lysosomal degradation. Examples include glycogen in the case of Pompe disease, glycosaminoglycans in the case of the mucopolysaccharidoses, glycoproteins in the cases of the oligosaccharidoses, and sphingolipids in the cases of Niemann-Pick disease types A and B, Gaucher disease, Tay-Sachs disease, Krabbe disease, and metachromatic leukodystrophy. Sometimes, the lysosomal storage can be caused not by the enzymatic deficiency of one of the hydrolases, but by the deficiency of an activator protein, as occurs in the AB variant of GM2 gangliosidosis. Still other times, the accumulated lysosomal material results from failed egress of a small molecule as a consequence of a deficient transporter, as in cystinosis or Salla disease. In the last couple of decades, enzyme replacement therapy has become available for a number of lysosomal storage diseases. Examples include imiglucerase, taliglucerase and velaglucerase for Gaucher disease, laronidase for Hurler disease, idursulfase for Hunter disease, elosulfase for Morquio disease, galsulfase for Maroteaux-Lamy disease, alglucosidase alfa for Pompe disease, and agalsidase alfa and beta for Fabry disease. In addition, substrate reduction therapy has been approved for certain disorders, such as eliglustat for Gaucher disease. The advent of treatment options for some of these disorders has led to newborn screening pilot studies, and ultimately to the addition of Pompe disease and Hurler disease to the Recommended Uniform Screening Panel (RUSP) in 2015 and 2016, respectively.

Report of interstitial 22q13.1q13.2 microduplication in two siblings with distinctive dysmorphic features, heart defect and mental retardation

We present two siblings (a boy and a girl) with a submicroscopic 4 Mb duplication at 22q13.1q13.2. Both children manifested infantile hypotonia and delayed motor milestones, congenital heart defect, growth deficiency, and strikingly similar and distinctive craniofacial dysmorphism including brachycephaly, blepharophimosis, short broad-based nose and wide mouth with thin upper lip. The boy had also a submucous cleft palate. Both had fair skin and hair compared with their parents. Both had moderate mental retardation associated with a short attention span. A 4-Mb interstitial duplication at 22q13.1q13.2 was detected by whole genome microarray comparative genomic hybridisation (array CGH) in both children. The duplication was confirmed by fluorescence in situ hybridisation (FISH) analysis. Their parents had normal array CGH results. FISH analysis revealed that the father was a carrier of a balanced interchromosomal submicroscopic insertion of 22q13 into chromosome 11q23, explaining the unbalanced aberration detected in both children. This report narrows down the critical region at 22q13.1q13.2, which is associated with mental retardation, pre- and post-natal growth retardation, hippocampal malformation, psychiatric symptoms such as short attention span and facial dysmorphism including hypertelorism, epicanthal folds and low set/abnormal ears.

Chip electrospray mass spectrometry for carbohydrate analysis

Currently two types of chip systems are used in conjunction with MS: out-of-plane devices, where hundreds of nozzles, nanospray emitters are integrated onto a single silicon substrate from which electrospray is established perpendicular to the substrate, and planar microchips, embedding a microchannel at the end of which electrospray is generated in-plane, on the edge of the microchip. In the last two years, carbohydrate research greatly benefited from the introduction and implementation of the chip-based MS. In two laboratories the advantages of the chip electrospray in terms of ionization efficiency, sensitivity, reproducibility, quality of data in combination with high mass accuracy, and resolution of detection were systematically explored for several carbohydrate classes: O- and N-glycopeptides, oligosaccharides, gangliosides and glycoprotein-derived O- and N-glycans, and glycopeptides. The current state-of-the-art in interfacing the chip electrospray devices to high-performance MS for carbohydrate analysis, and the particular requirements for method optimization in both positive and negative ion modes are reviewed here. The recent applications of these miniaturized devices and their general potential for glycomic-based surveys are highlighted.

Sheathless reverse-polarity capillary electrophoresis-electrospray-mass spectrometry for analysis of underivatized glycoconjugates

We report on the development of a novel methodology to extend the limits of capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) general applicability. A sheathless on-line CE-ESI-MS setup was optimized on standard monosaccharide mixture to operate in reverse polarity and negative ion mode for MS detection without pressure to assist the sample migration, coating of the capillaries, and/or sample derivatization. This approach was further applied for screening of a complex glycopeptide mixture obtained from the urine of a patient diagnosed with N-acetylhexosaminidase deficiency, known as Schindler's disease. The potential of this methodology in terms of high sensitivity, separation efficiency, resolution, and reproducibility is demonstrated. In combination with the high quality of MS data, a new, significantly improved insight into the sample heterogeneity is possible.

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.

Coupling of fully automated chip electrospray to Fourier transform ion cyclotron resonance mass spectrometry for high-performance glycoscreening and sequencing

The NanoMate robot has been coupled to a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer at 9.4 T and implemented for the first time for complex carbohydrate analysis. It was optimized in the negative ion mode to achieve automated sample delivery on the chip along with increased sensitivity, ultra-high resolution and accurate mass determination. A novel bracket has been designed to allow a reliable mounting of the NanoMate to the Apollo electrospray ionization (ESI) source of an APEX II instrument. The notably higher efficiency of ionization for compositional mapping of complex mixtures and feasibility for fragmentation analysis of components by sustained off-resonance irradiation collision-induced tandem mass spectrometry (SORI-CID MS2) has been demonstrated on a glycoconjugate mixture containing O-glycosylated sialylated peptides from urine of a patient suffering from a hereditary N-acetylhexosaminidase deficiency (Schindler's disease), previously analyzed by capillary-based nanoESI-FTICRMS, and of a healthy control person. Due to its potential to generate highly charged ionic species, reduce the in-source fragmentation, increase sensitivity, reproducibility and ionization efficiency, along with the ability to generate a sustained and constant electrospray, this method can be considered as a new platform for advanced glycomics.

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.

Defects in degradation of blood group A and B glycosphingolipids in Schindler and Fabry diseases

Skin fibroblast cultures from patients with inherited lysosomal enzymopathies, alpha-N-acetylgalactosaminidase (alpha-NAGA) and alpha-galactosidase A deficiencies (Schindler and Fabry disease, respectively), and from normal controls were used to study in situ degradation of blood group A and B glycosphingolipids. Glycosphingolipids A-6-2 (GalNAc (alpha 1-->3)[Fuc alpha 1-->2]Gal(beta1-->4)GlcNAc(beta 1-->3)Gal(beta 1--> 4)Glc (beta 1-->1')Cer, IV(2)-alpha-fucosyl-IV(3)-alpha-N-acetylgalactosaminylneolactotetraosylceramide), B-6-2 (Gal(alpha 1-->3)[Fuc alpha 1--> 2] Gal (beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc(beta 1-->1')Cer, IV(2)- alpha-fucosyl-IV(3)-alpha-galactosylneolactotetraosylceramide), and globoside (GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc(beta 1-->1') Cer, globotetraosylceramide) were tritium labeled in their ceramide moiety and used as natural substrates. The degradation rate of glycolipid A-6-2 was very low in fibroblasts of all the alpha-NAGA-deficient patients (less than 7% of controls), despite very heterogeneous clinical pictures, ruling out different residual enzyme activities as an explanation for the clinical heterogeneity. Strongly elevated urinary excretion of blood group A glycolipids was detected in one patient with blood group A, secretor status (five times higher than upper limit of controls), in support of the notion that blood group A-active glycolipids may contribute as storage compounds in blood group A patients. When glycolipid B-6-2 was fed to alpha-galactosidase A-deficient cells, the degradation rate was surprisingly high (50% of controls), while that of globotriaosylceramide was reduced to less than 15% of control average, presumably reflecting differences in the lysosomal enzymology of polar glycolipids versus less-polar ones. Relatively high-degree degradation of substrates with alpha-D-Galactosyl moieties hints at a possible contribution of other enzymes.

Etiology and pathophysiology of autistic behavior: clues from two cases with an unusual variant of neuroaxonal dystrophy

Two unrelated individuals with autistic behavior had numerous swollen axon terminals (spheroids) located in specific brain regions relevant to their behavioral symptoms. Spheroids are characteristic of neuroaxonal dystrophy, but the clinical profile and anatomic distribution of the lesions in these two patients differed from those of previously described patients with neuroaxonal dystrophy. Spheroids were numerous in the sensory nuclei of the spinal cord and medulla, specific nuclei and the reticular formation of the brainstem tegmentum, hypothalamus, anterior and dorsomedial thalamus, hippocampus, and cingulate and orbitofrontal cortices. Spheroids were sparse in the primary and association cortices and basal ganglia and absent in the hemispheric white matter. Cerebellar atrophy was present in both cases but associated with spheroids in only one case. These cases represent a new variant of neuroaxonal dystrophy in which behavioral symptoms characteristic of autism dominated the clinical picture. Neuroaxonal dystrophy should be included in the list of diseases that may be found in persons with autism.

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.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Cerebral glucose metabolism in type I alpha-N-acetylgalactosaminidase deficiency: an infantile neuroaxonal dystrophy

Cerebral glucose metabolism was investigated in a 4.8-year-old boy with alpha-N-acetylgalactosaminidase deficiency using 2-[18F]fluoro-2-deoxy-D-glucose and positron emission tomography (PET). In comparison to normal values for age, the overall cerebral glucose metabolism was reduced and the regional cerebral glucose metabolism was decreased in proportion to the degree of atrophy. In the supratentorial cortical regions, the hypometabolism was asymmetric. However, the level of regional cerebral glucose metabolism in all cortical regions excluded a persistent vegetative state. In the lentiform nucleus and the head of the caudate, comparatively increased regional cerebral glucose metabolism was documented, similar to findings in neurodegenerative disorders with active epilepsy. In contrast, the infratentorial structures (cerebellar hemispheres, brain stem, mesencephalon, and hypothalamus), which are predominantly affected by the atrophic process, showed distinct and symmetric hypometabolism. Thus, the 2-[18F]-fluoro-2-deoxy-D-glucose PET scans provided additional insight into and correlation of the functional and structural disturbances in type I alpha-N-acetylgalactosaminidase deficiency, in addition to documenting the hypometabolism due to brain atrophy.

Molecular cloning, structural organization, sequence, chromosomal assignment, and expression of the mouse alpha-N-acetylgalactosaminidase gene

Alpha-N-acetylgalactosaminidase (2-acetamido-2-deoxy-alpha-d-galactoside acetamidodeoxy-galactohydrolase, NAGA; EC 3.2.1.49) deficiency is a recently recognized autosomal recessive lysosomal disease. As a prerequisite for the generation of an animal model, the mouse NAGA gene was cloned and characterized. The NAGA gene was assigned to mouse chromosome 15 band E3, syntenic to the region encompassing the human gene, and NAGA-deficient mutant human cells transfected with the cosmid clone containing the mouse NAGA gene expressed NAGA activity. Comparison of the mouse NAGA nucleotide sequence with the human NAGA sequence predicted that the mouse NAGA gene contains an open reading frame of 1245bp, comprising nine coding exons and spanning a genomic region of 8258bp, and a 3' untranslated region of 0.5kb. The 5' untranslated region was determined in primer extension studies to be 235bp in length. Nucleotide identity between the human and mouse NAGA exons ranged from 67.4 to 89.5%, with better matches for exons 1-7 than for 8 and 9. The overall amino acid identity between the mouse and human deduced NAGA polypeptides was 82.0%, between those of mouse and chicken 72.9%. Homology was found to only one other mouse gene, i.e. the alpha-galactosidase A (GALA; EC 3.2.1. 22) gene. The amino acid identity ranged from 51.6 to 62.1% in the polypeptide regions corresponding to NAGA exons 2-7 and GALA exons 1-6, but little, if any, in the remainder. These analyses gave emphasis to the strong conservation of the NAGA gene and its origin from an ancestor common with the GALA gene, with NAGA exons 8 and 9 and GALA exon 7 being the most divergent regions in the evolution of the two genes.

Oligosaccharide excretion in adult Gaucher disease

Gaucher disease is a lysosomal storage disease characterized by storage of glucocerebroside due to lysosomal glucocerebrosidase deficiency. Increased urinary excretion of sialyloligosaccharides and mannosylglycoasparagines has been described for two patients with the infantile form of the disease, probably as a consequence of obstruction of lysosomal functioning due to the glycolipid accumulation in lysosomes. By thin-layer chromatography, we found increased urinary oligosaccharide excretion in a series of adult non-neuronopathic patients. Oligosaccharide patterns were comparable between patients and also with the pattern observed in infantile Gaucher disease. Composition was analysed by methanolysis and gas chromatography. Mannose and N-acetylglucosamine are the main carbohydrates in all oligosaccharide bands. A statistically significant correlation was found between oligosaccharide excretion and the severity of the disease expressed as severity score index. Patients treated with enzyme replacement therapy showed a reduction up to 65% of the original oligosaccharide excretion after 1 year of treatment, comparable with the reduction in spleen volume.

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.

Neuroaxonal dystrophy in infantile alpha-N-acetylgalactosaminidase deficiency

Morphologic alterations in biopsies of central and peripheral nervous tissue were investigated at the light-and electron-microscopic level in the first cases of lysosomal alpha-N-acetylgalactosaminidase deficiency. Widespread spheroid formation was observed in terminal and preterminal axons. Neocortical and peripheral autonomic axons contained tubulovesicular and lamelliform membranous arrays, prominent acicular clefts, and electron-dense axoplasmic matrix, the typical ultrastructural abnormalities corresponding to axonal spheroids in many inherited and acquired axonopathies. Central and peripheral membranous distal axonal spheroids were the only neuropathologic abnormality identified; other alterations resembling those in various neuronopathic lysosomal storage diseases were not observed. The morphologic findings and the distribution of the lesion in the present disorder are remarkably similar to those reported in the inherited infantile form of neuroaxonal dystrophy with normal alpha-N-acetylgalactosaminidase activity (Seitelberger disease).