[A case of GM1 gangliosidoses].

This article describes a case which seek medical advice for 2 months due to retrogressive development, The discovery of the characteristic fundus of the macular cherry-red spot is a key clue for further genetic analysis, GLB compound heterozygous mutations is detected, and enzymology results show that the acid B-galactose glucoside enzyme significantly decrease, fundus inspection help diagnosis GM1 gangliosidoses.

Gene-Based Approaches to Inherited Neurometabolic Diseases.

In the last decade, the gene therapy (GT) field experienced a renaissance, thanks to crucial understandings and innovations in vector design, stem cell manipulation, conditioning protocols, and cell/vector delivery. These efforts were successfully coupled with unprecedented clinical results of the trials employing the newly developed technology and with the novel establishment of academic-industrial partnerships. A renewed and strengthened interest is rising in the development of gene-based approaches for inherited neurometabolic disorders with severe neurological involvement. Inherited metabolic disorders are monogenetic diseases caused by enzymatic or structural deficiencies affecting the lysosomal or peroxisomal metabolic activity. The metabolic defect can primarily affect the central nervous system, leading to neuronal death, microglial activation, inflammatory demyelination, and axonal degeneration. This review provides an overview of the GT strategies currently under clinical investigation for neurometabolic lysosomal and peroxisomal storage diseases, such as adrenoleukodystrophy and metachromatic leukodystrophy, as well as novel emerging indications such as mucopolysaccharidoses, gangliosidoses, and neuronal ceroid lipofuscinoses, with a comprehensive elucidation of the main features and mechanisms at the basis of a successful GT approach for these devastating diseases.

Genotype, phenotype and in silico pathogenicity analysis of HEXB mutations: Panel based sequencing for differential diagnosis of gangliosidosis.

OBJECTIVES: Gangliosidosis is an inherited metabolic disorder causing neurodegeneration and motor regression. Preventive diagnosis is the first choice for the affected families due to lack of straightforward therapy. Genetic studies could confirm the diagnosis and help families for carrier screening and prenatal diagnosis. An update of HEXB gene variants concerning genotype, phenotype and in silico analysis are presented. PATIENTS AND METHODS: Panel based next generation sequencing and direct sequencing of four cases were performed to confirm the clinical diagnosis and for reproductive planning. Bioinformatic analyses of the HEXB mutation database were also performed. RESULTS: Direct sequencing of HEXA and HEXB genes showed recurrent homozygous variants at c.509G>A (p.Arg170Gln) and c.850C>T (p.Arg284Ter), respectively. A novel variant at c.416T>A (p.Leu139Gln) was identified in the GLB1 gene. Panel based next generation sequencing was performed for an undiagnosed patient which showed a novel mutation at c.1602C>A (p.Cys534Ter) of HEXB gene. Bioinformatic analysis of the HEXB mutation database showed 97% consistency of in silico genotype analysis with the phenotype. Bioinformatic analysis of the novel variants predicted to be disease causing. In silico structural and functional analysis of the novel variants showed structural effect of HEXB and functional effect of GLB1 variants which would provide fast analysis of novel variants. CONCLUSIONS: Panel based studies could be performed for overlapping symptomatic patients. Consequently, genetic testing would help affected families for patients' management, carrier detection, and family planning's.

Gangliosidoses.

The gangliosidoses comprise a family of lysosomal storage diseases characterized by the accumulation of complex glycosphingolipids in the nervous system and other tissues, secondary to the deficient activity of lysosomal hydrolases or their associated activator proteins. GM1 and GM2 gangliosidosis are associated with deficiency of ß-galactosidase and ß-hexosaminidase respectively. All gangliosidoses are characterized by progressive neurodegeneration, the severity of which is proportional to the residual enzyme activity. The GM1 gangliosidoses are characterized by dysostosis, organomegaly and coarsening in their most severe forms, whereas children with classic infantile GM2 gangliosidosis (Tay-Sachs disease) are usually spared systemic involvement, except in the case of the Sandhoff variant, in which organomegaly may occur. Cherry-red macular spots occur in the early onset forms of the gangliosidoses, but are less frequently seen in the less severe, later onset phenotypes. Macrocephaly, an exaggerated startle response, cognitive decline, seizures, ataxia, and progressive muscular atrophy may occur in different forms of gangliosidosis. The diagnosis is made by assay of enzyme activity, and can be confirmed by mutation analysis. Carrier screening for Tay-Sachs disease has been remarkably successful in reducing the incidence of this disease in the at-risk Ashkenazi population. There are no proven disease-modifying therapies for the gangliosidoses.

Elastogenesis in cultured dermal fibroblasts from patients with lysosomal beta-galactosidase, protective protein/cathepsin A and neuraminidase-1 deficiencies.

The human GLB1 gene encodes a lysosomal beta-galactosidase (beta-Gal) and an elastin-binding protein (EBP). Defect of the EBP as a chaperon for tropoelastin and a component of receptor complex among neuraminidase-1 (NEU1) and protective protein/cathepsin A (PPCA) is suggested responsible for impaired elastogenesis in autosomal recessive beta-Gal, PPCA and NEU1 deficiencies. The purpose of this study is to determine effects of GLB1, PPCA and NEU1 gene mutations on elastogenesis in skin fibroblasts. Elastic fiber formation and the EBP mRNA expression were examined by immunofluorescence with an anti-tropoelastin antibody and RT-PCR selective for EBP in skin fibroblasts with these lysosomal enzyme deficiencies. Apparently normal elastogenesis and EBP mRNA expression were observed for fibroblasts from Morquio B disease cases with the GLB1 gene alleles (W273L/W273L, W273L/R482H and W273L/W509C substitutions, respectively), a galactosialidosis case with the PPCA allele (IVS7+3A/IVS7+3A) and a sialidosis case with the NEU1 allele (V217M/G243R) as well as normal subject. In this study, the W273L substitution in the EBP could impossibly cause the proposed defect of elastogenesis, and the typical PPCA splicing mutation and the V217M/G243R substitutions in the NEU1 might hardly have effects on elastic fiber formation in the dermal fibroblasts.

Crystallographic evidence for substrate-assisted catalysis in a bacterial beta-hexosaminidase.

beta-Hexosaminidase, a family 20 glycosyl hydrolase, catalyzes the removal of beta-1,4-linked N-acetylhexosamine residues from oligosaccharides and their conjugates. Heritable deficiency of this enzyme results in various forms of GalNAc-beta(1,4)-[N-acetylneuraminic acid (2,3)]-Gal-beta(1,4)-Glc-ceramide gangliosidosis, including Tay-Sachs disease. We have determined the x-ray crystal structure of a beta-hexosaminidase from Streptomyces plicatus to 2.2 A resolution (Protein Data Bank code ). beta-Hexosaminidases are believed to use a substrate-assisted catalytic mechanism that generates a cyclic oxazolinium ion intermediate. We have solved and refined a complex between the cyclic intermediate analogue N-acetylglucosamine-thiazoline and beta-hexosaminidase from S. plicatus to 2.1 A resolution (Protein Data Bank code ). Difference Fourier analysis revealed the pyranose ring of N-acetylglucosamine-thiazoline bound in the enzyme active site with a conformation close to that of a (4)C(1) chair. A tryptophan-lined hydrophobic pocket envelopes the thiazoline ring, protecting it from solvolysis at the iminium ion carbon. Within this pocket, Tyr(393) and Asp(313) appear important for positioning the 2-acetamido group of the substrate for nucleophilic attack at the anomeric center and for dispersing the positive charge distributed into the oxazolinium ring upon cyclization. This complex provides decisive structural evidence for substrate-assisted catalysis and the formation of a covalent, cyclic intermediate in family 20 beta-hexosaminidases.

Thermodynamic characterisation of the mutated isoenzyme A of beta-N-acetylhexosaminidase in GM2-gangliosidosis B1 variant.

Here we report the determination of the activation energies of the plasma isoenzymes of beta-N-acetylhexosaminidase (Hex, EC 3.2.1.52), isolated by chromatography in DEAE-cellulose, using the neutral chromogenic substrate 3,3'dichlorophenylsulfonphthaleinyl-N-acetyl-beta-D-glucosaminide. The activation energy of mutated Hex A isoenzyme (Ea approximately 71.5 kJ/mol) from a patient with GM2-gangliosidosis B1 variant, homozygote for the G533-->A (Arg178His) mutation, was significantly higher than that of normal Hex A (Ea approximately 41.8 kJ/mol) and analogous to that of Hex B isoenzyme (Ea approximately 75.1 kJ/mol). The determination of this thermodynamic variable of Hex in different biological specimens could allow for a straightforward biochemical characterisation of the GM2-gangliosidosis B1 variant.

GM2 gangliosidosis AB variant: clinical and biochemical studies of a Japanese patient.

OBJECTIVE: To determine the clinical features and biochemical basis of the first Japanese patient with the GM2 gangliosidosis AB variant. METHODS: The clinical manifestations and laboratory findings in the patient were investigated. Cultured fibroblasts from the patient were analyzed by means of immunofluorescence staining with an anti-GM2 ganglioside monoclonal antibody and thin-layer chromatography and immunostaining. GM1 ganglioside catabolism in cultured cells was analyzed by pulse labeling, and the amount of GM2 activator in cells was determined by Western blot analysis. Gene analysis was performed according to standard protocols. RESULTS: The patient showed progressive neurologic manifestations of quite early onset. Muscular weakness and hypotonia became evident by 1 month of age, and the patient then developed a startle reaction, severe psychomotor retardation, and myoclonic seizures. Immunocytochemical analysis clearly revealed the accumulation of GM2 ganglioside in cultured fibroblasts from the patient, and thin-layer chromatography confirmed it. Western blot and metabolic studies showed a complete deficiency of GM2 activator. Gene analysis did not reveal any mutations in the protein coding region of the GM2 activator gene. CONCLUSION: The clinical features and biochemical basis of this Japanese patient with GM2 gangliosidosis AB variant were determined. Immunocytochemical analysis using cultured fibroblasts as samples is available for the diagnosis of this disease.

Complete localization of disulfide bonds in GM2 activator protein.

Lysosomal degradation of ganglioside GM2 by hexosaminidase A requires the presence of a small, non-enzymatic cofactor, the GM2-activator protein (GM2AP). Lack of functional protein leads to the AB variant of GM2-gangliosidosis, a fatal lysosomal storage disease. Although its possible mode of action and functional domains have been discussed frequently in the past, no structural information about GM2AP is available so far. Here, we determine the complete disulfide bond pattern of the protein. Two of the four disulfide bonds present in the protein were open to classical determination by enzymatic cleavage and mass spectrometry. The direct localization of the remaining two bonds was impeded by the close vicinity of cysteines 136 and 138. We determined the arrangement of these disulfide bonds by MALDI-PSD analysis of disulfide linked peptides and by partial reduction, cyanylation and fragmentation in basic solution, as described recently (Wu F, Watson JT, 1997, Protein Sci 6:391-398).

Biochemical characterization of the Cys138Arg substitution associated with the AB variant form of GM2 gangliosidosis: evidence that Cys138 is required for the recognition of the GM2 activator/GM2 ganglioside complex by beta-hexosaminidase A.

The function of the GM2 activator protein is to act as a substrate-specific cofactor in the hydrolysis of GM2 ganglioside by beta-hexosaminidase A. Mutations in the gene encoding it result in the AB variant form of GM2 gangliosidosis. One such mutation, Cys138 Arg, results in the mutant protein being retained and degraded in the endoplasmic reticulum of mammalian cells. In order to characterize the biochemical effects of this substitution, we expressed the mutant protein in transformed bacteria. We first compared the wild-type protein produced by two bacterial expression methods, one requiring protein refolding, with activator purified from the medium of transfected CHO cells. The "activity" and circular dichroism spectrum (alpha-helical content) of all three proteins were similar, justifying the use of refolded activator from transformed bacteria in structure/function studies. Second, the mutant protein was expressed in both bacterial systems and in each retained approximately 2% of the wild type's specific activity. The presence of even this small amount of activity in the mutant protein coupled with a calculated alpha-helical content nearly identical to the wild type, strongly suggest that no major tertiary or secondary structural changes, respectively, had occurred due to the mutation. However, we demonstrate that its heat stability at 60 degrees C is reduced 14-fold, suggesting some localized change in tertiary structure. The loss of a disulfide loop was confirmed by reacting the mutant protein with Ellman's reagent. A kinetic analysis detected a large increase in the apparent K(m) of beta-hexosaminidase A for the mutant; however, there was no apparent change in Vmax. A fluorescence dequenching assay was used to evaluate the ability of the mutant protein to transport lipids and bind GM2 ganglioside. These assays detected no difference between the wild-type and mutant proteins, indicating that the Cys138 Arg substitution has no effect on these functions. We conclude that the mutation specifically affects a domain in the activator protein that is responsible for the recognition of the activator-GM2 ganglioside complex by beta-hexosaminidase A.

Mouse models of human lysosomal diseases.

Genetically authentic animal models of human lysosomal diseases occur spontaneously in many mammalian species. However, most are among larger domestic or farm animals with only two well-defined genetic lysosomal diseases known among rodents. This status changed dramatically in recent years with the advent of the combined homologous recombination and embryonic stem cell technology, which allows directed generation of mouse models that are genetically equivalent to human diseases. Almost all known human sphingolipidoses, two mucopolysaccharidoses and aspartylglycosaminuria have so far been duplicated in mice and more are expected in the near future. This technology also allows generation of mouse mutants that are not known or are highly unlikely to exist in humans, such as "double-knockouts." These animal models will play an important role in studies of the pathogenesis and treatment of these disorders. While the utility of these mouse models is obvious, species differences in brain development and metabolic pathways must be always remembered, if the ultimate goal of the study is application to human patients.

Apoptotic cell death in mouse models of GM2 gangliosidosis and observations on human Tay-Sachs and Sandhoff diseases.

Tay-Sachs and Sandhoff diseases are autosomal recessive neurodegenerative diseases resulting from the inability to catabolize GM2 ganglioside by beta-hexosaminidase A (Hex A) due to mutations of the alpha subunit (Tay-Sachs disease) or beta subunit (Sandhoff disease) of Hex A. Hex B (beta beta homodimer) is also defective in Sandhoff disease. We previously developed mouse models of both diseases and showed that Hexa-/- (Tay-Sachs) mice remain asymptomatic to at least 1 year of age while Hexb-/- (Sandhoff) mice succumb to a profound neurodegenerative disease by 4-6 months of age. Here we find that neuron death in Hexb-/- mice is associated with apoptosis occurring throughout the CNS, while Hexa-/- mice were minimally involved at the same age. Studies of autopsy samples of brain and spinal cord from human Tay-Sachs and Sandhoff diseases revealed apoptosis in both instances, in keeping with the severe expression of both diseases. We suggest that neuron death is caused by unscheduled apoptosis, implicating accumulated GM2 ganglioside or a derivative in triggering of the apoptotic cascade.

Mouse model of GM2 activator deficiency manifests cerebellar pathology and motor impairment.

The GM2 activator deficiency (also known as the AB variant), Tay-Sachs disease, and Sandhoff disease are the major forms of the GM2 gangliosidoses, disorders caused by defective degradation of GM2 ganglioside. Tay-Sachs and Sandhoff diseases are caused by mutations in the genes (HEXA and HEXB) encoding the subunits of beta-hexosaminidase A. The GM2 activator deficiency is caused by mutations in the GM2A gene encoding the GM2 activator protein. For degradation of GM2 ganglioside by beta-hexosamindase A, the GM2 activator protein must participate by forming a soluble complex with the ganglioside. In each of the disorders, GM2 ganglioside and related lipids accumulate to pathologic levels in neuronal lysosomes, resulting in clinically similar disorders with an onset in the first year of life, progressive neurodegeneration, and death by early childhood. We previously have described mouse models of Tay-Sachs (Hexa -/-) and Sandhoff (Hexb -/-) diseases with vastly different clinical phenotypes. The Hexa -/- mice were asymptomatic whereas the Hexb -/- mice were severely affected. Through gene disruption in embryonic stem cells we now have established a mouse model of the GM2 activator deficiency that manifests an intermediate phenotype. The Gm2a -/- mice demonstrated neuronal storage but only in restricted regions of the brain (piriform, entorhinal cortex, amygdala, and hypothalamic nuclei) reminiscent of the asymptomatic Tay-Sachs model mice. However, unlike the Tay-Sachs mice, the Gm2a -/- mice displayed significant storage in the cerebellum and defects in balance and coordination. The abnormal ganglioside storage in the Gm2a -/- mice consisted of GM2 with a low amount of GA2. The results demonstrate that the activator protein is required for GM2 degradation and also may indicate a role for the GM2 activator in GA2 degradation.

Spongecake and eggroll: two hereditary diseases in Drosophila resemble patterns of human brain degeneration.

Various neuronal degenerative diseases are characterized by late onset, relentless progression, and finally death. Many have a direct genetic basis; others are of still unknown etiological mechanisms [1,2]. The study of human neurodegenerative diseases is complicated by the difficulty of obtaining tissue samples at various stages of progression, especially early in the course of the disease. Since neurodegeneration occurs in many organisms [3-5], model organisms amenable to genetic and molecular techniques, such as the mouse, offer important advantages. Much less laborious and expensive are worms or flies, which have short generation times and can be rapidly screened for mutations. To investigate the use of the fly as a model system for identifying genes related to such diseases, we screened for mutants having reduced lifespan, then examined them for brain degeneration. We describe here two such mutants, each with a different pattern of degeneration as characterized by light and transmission electron microscopy. The brain of the aging spongecake mutant exhibits regionally specific, membrane-bound vacuoles similar to those seen in spongiform degenerations such as Creutzfeldt-Jakob disease [6,7]. The mutant eggroll develops dense, multilamellated structures in the brain, resembling ones found in lipid storage diseases such as Tay-Sachs [8].

Heritability and biochemistry of gangliosidosis in emus (Dromaius novaehollandiae).

The progeny of two emu breeder pairs, which had a history of producing offspring with gangliosidosis, were monitored for 15 mo. DNA fingerprinting revealed that individuals in each breeder pair were not related to each other. One breeder pair had 13 progeny that reached or exceeded the age of 1 mo, and six of these progeny developed gangliosidosis. The mean age at which these affected emus were euthanatized, with distinct neurologic disease, or died was 5.7 mo. The second emu pair had 13 progeny, seven of which developed gangliosidosis, with a mean age of euthanasia/death of 4.6 mo. Affected emus died or were euthanatized from 2 to 8 mo of age. The primary clinical sign in the affected emus was mild to severe ataxia. Severe hemorrhage into the body cavity or the muscles of the thigh was noted in 8 of 13 of the affected emus. Brain ganglioside levels were evaluated in six of the affected emus and six controls. Significant increases (P < 0.05) in gangliosides GM1 and GM3 were noted, with 2.3- and 4.9-fold increases in these two gangliosides, respectively, in affected emus. Furthermore, the diseased emu brains contained ganglioside GM2, whereas this monosialoganglioside was undetectable in the brains of normal controls. Total mean brain ganglioside sialic acid in affected emus was increased 3.3-fold in comparison with controls. Serum chemistries revealed elevated cholesterol and decreased uric acid levels in affected emus. Gangliosidosis in emus is an inherited disease process that, in the current study, caused 50% mortality in the progeny of two emu breeder pairs. The elimination of this lethal gene from emu breeder stock is essential for the long-term economic viability of the United States emu industry.

The beta-hexosaminidase deficiency disorders: development of a clinical paradigm in the mouse.

Tay-Sachs disease and Sandhoff disease are severe neurodegenerative disorders caused by a deficiency of beta-hexosaminidase A and resultant accumulation of its substrate, GM2 ganglioside, in neuronal lysosomes. The three clinical forms of the disorders (infantile, juvenile and adult) are of varying severity and onset, and have been correlated with the amount of residual GM2 ganglioside-degrading activity present in patients' cells. Through targeted disruption of the murine beta-hexosaminidase genes in embryonic stem cells, we have developed a set of mice that vary in their GM2 ganglioside-degrading capacity and exhibit many of the clinical features of the human diseases. These mice are valuable for the study of pathogenic mechanisms and for devising novel therapeutic strategies in these disorders.

[Sialidosis and galactosialidosis as the cause of non-immunologic hydrops fetalis]. / Sialidose und Galaktosialidose als Ursache des nicht-immunologischen Hydrops fetalis.

Two cases of non-immunological hydrops fetalis (NIHF) presenting with massive ascites are reported; in both patients an oligosaccharid-pattern in the urine typical for sialidosis resp. galactosialidosis was found. The cerebral sonography of both patients showed streaky echo enhancement in the region of the thalamostriatal vessels, which was interpreted as calcification of the vessels. The courses of the patients were characterised by recurrent infections, hepatosplenomegaly and myoclonus. Relevant literature reports on a large variability in the clinical appearance of oligosaccharidoses. The diagnosis of sialidosis is confirmed in cultured fibroblasts by the deficiency of alpha-N-acetylneuraminidase and, in case of galactosialidosis by the additional lack of beta-galactosidase. The precise diagnosis in NIHF is of increasing interest for prenatal diagnostic as well as for neonatological management.

Molecular analysis of a GM2-activator deficiency in two patients with GM2-gangliosidosis AB variant.

Lysosomal degradation of ganglioside GM2 by beta-hexosaminidase A (hex A) requires the presence of the GM2 activator protein (GM2AP) as an essential cofactor. A deficiency of the GM2 activator causes the AB variant of GM2 gangliosidosis, a recessively inherited disorder characterized by excessive neuronal accumulation of GM2 and related glycolipids. Two novel mutations in the GM2 activator gene (GM2A) have been identified by the reverse-transcriptase-PCR method--a three-base deletion, AAG262-264, resulting in a deletion of Lys88, and a single-base deletion, A410, that causes a frameshift. The latter results in substitution of 33 amino acids and the loss of another 24 amino acid residues. Both patients are homoallelic for their respective mutations inherited from their parents, who are heteroallelic at the GM2A locus. Although the cultured fibroblasts of both patients produce normal levels of activator mRNA, they lack a lysosomal form of GM2AP. Pulse/chase labeling of cultured fibroblasts of the patients, in presence and absence of brefeldin A, indicates a premature degradation of both--mutant and truncated--GM2APs in the endoplasmic reticulum or Golgi. These results were supported by in vitro translation experiments and expression of the mutated proteins. When the mutated GM2APs were expressed in Escherichia coli, both mature GM2AP forms turned proved to exhibit only residual activities in an in vitro assay.

Mice lacking both subunits of lysosomal beta-hexosaminidase display gangliosidosis and mucopolysaccharidosis.

The GM2 gangliosidoses, Tay-Sachs and Sandhoff diseases, are caused by mutations in the HEXA (alpha-subunit) and HEXB (beta-subunit) genes, respectively. Each gene encodes a subunit for the heterodimeric lysosomal enzyme, beta-hexosaminidase A (alpha beta), as well as for the homodimers beta-hexosaminidase B (beta beta) and S (alpha alpha). In this study, we have produced mice that have both Hexa and Hexb genes disrupted through interbreeding Tay-Sachs (Hexa-/-) and Sandhoff (Hexb-/-) disease model mice. Lacking both the alpha and beta-subunits these 'double knockout' mice displayed a total deficiency of all forms of lysosomal beta-hexosaminidase including the small amount of beta-hexosaminidase S present in the Sandhoff disease model mice. More surprisingly, these mice showed the phenotypic, pathologic and biochemical features of the mucopolysaccharidoses, lysosomal storage diseases caused by the accumulation of glycosaminoglycans. The mucopolysaccharidosis phenotype is not seen in the Tay-Sachs or Sandhoff disease model mice or in the corresponding human patients. This result demonstrates that glycosaminoglycans are crucial substrates for beta-hexosaminidase and that their lack of storage in Tay-Sachs and Sandhoff diseases is due to functional redundancy in the beta-hexosaminidase enzyme system.