Form Of GM2 Gangliosidosis Research Articles

Pontocerebellar atrophy is the hallmark neuroradiological finding in late-onset Tay-Sachs disease.

Late-onset Tay-Sachs disease (LOTS) is a form of GM2 gangliosidosis, an autosomal recessive neurodegenerative disorder characterized by slowly progressive cerebellar ataxia, lower motor neuron disease, and psychiatric impairment due to mutations in the HEXA gene. The aim of our work was to identify the characteristic brain MRI findings in this presumably underdiagnosed disease. Clinical data and MRI findings from 16 patients (10F/6M) with LOTS from two centers were independently assessed by two readers and compared to 16 age- and sex-related controls. Lower motor neuron disease (94%), psychiatric symptoms-psychosis (31%), cognitive impairment (38%) and depression (25%)-and symptoms of cerebellar impairment including dysarthria (94%), ataxia (81%) and tremor (69%), were the most common clinical features. On MRI, pontocerebellar atrophy was a constant finding. Compared to controls, LOTS patients had smaller mean middle cerebellar peduncle diameter (p < 0.0001), mean superior cerebellar peduncle diameter (p = 0.0002), mesencephalon sagittal area (p = 0.0002), pons sagittal area (p < 0.0001), and larger 4th ventricle transversal diameter (p < 0.0001). Mild corpus callosum thinning (37.5%), mild cortical atrophy (18.8%), and white matter T2 hyperintensities (12.5%) were also present. Given the characteristic clinical course and MRI findings of the pontocerebellar atrophy, late-onset Tay-Sachs disease should be considered in the differential diagnosis of adult-onset cerebellar ataxias.

Integrated Computational Analysis Highlights unique miRNA Signatures in the Subventricular Zone and Striatum of GM2 Gangliosidosis Animal Models.

This work explores for the first time the potential contribution of microRNAs (miRNAs) to the pathophysiology of the GM2 gangliosidosis, a group of Lysosomal Storage Diseases. In spite of the genetic origin of GM2 gangliosidosis, the cascade of events leading from the gene/protein defects to the cell dysfunction and death is not fully elucidated. At present, there is no cure for patients. Taking advantage of the animal models of two forms of GM2 gangliosidosis, Tay-Sachs (TSD) and Sandhoff (SD) diseases, we performed a microRNA screening in the brain subventricular zone (SVZ) and striatum (STR), which feature the neurogenesis and neurodegeneration states, respectively, in adult mutant mice. We found abnormal expression of a panel of miRNAs involved in lipid metabolism, CNS development and homeostasis, and neuropathological processes, highlighting region- and disease-specific profiles of miRNA expression. Moreover, by using a computational analysis approach, we identified a unique disease- (SD or TSD) and brain region-specific (SVZ vs. STR) miRNAs signatures of predicted networks potentially related to the pathogenesis of the diseases. These results may contribute to the understanding of GM2 gangliosidosis pathophysiology, with the aim of developing effective treatments.

Case reports of juvenile GM1 gangliosidosisis type II caused by mutation in GLB1 gene

BackgroundType II or juvenile GM1-gangliosidosis is an autosomal recessive lysosomal storage disorder, which is clinically distinct from infantile form of the disease by the lack of characteristic cherry-red spot and hepatosplenomegaly. The disease is characterized by slowly progressive neurodegeneration and mild skeletal changes. Due to the later age of onset and uncharacteristic presentation, diagnosis is frequently puzzled with other ataxic and purely neurological disorders. Up to now, 3–4 types of GM1-gangliosidosis have been reported and among them type I is the most common phenotype with the age of onset around 6 months. Various forms of GM1-gangliosidosis are caused by GLB1 gene mutations but severity of the disease and age of onset are directly related to the position and the nature of deleterious mutations. However, due to its unique genetic cause and overlapping clinical features, some researchers believe that GM1 gangliosidosis represents an overlapped disease spectrum instead of four distinct types.Case presentationHere, we report a less frequent type of autosomal recessive GM1 gangliosidosis with perplexing clinical presentation in three families in the southwest part of Iran, who are unrelated but all from “Lurs” ethnic background. To identify disease-causing mutations, Whole Exome Sequencing (WES) utilizing next generation sequencing was performed. Four patients from three families were investigated with the age of onset around 3 years old. Clinical presentations were ataxia, gate disturbances and dystonia leading to wheelchair-dependent disability, regression of intellectual abilities, and general developmental regression. They all were born in consanguineous families with no previous documented similar disease in their parents. A homozygote missense mutation in GLB1 gene (c. 601 G > A, p.R201C) was found in all patients. Using Sanger sequencing this identified mutation was confirmed in the proband, their parents, grandparents, and extended family members, confirming its autosomal recessive pattern of inheritance.ConclusionsOur study identified a rare pathogenic missense mutation in GLB1 gene in patients with complex neurodevelopmental findings, which can extend the list of differential diagnoses for childhood ataxia in Iranian patients.

Pathology of GM2 Gangliosidosis in Jacob Sheep

The G(M2) gangliosidoses are a group of lysosomal storage diseases caused by defects in the genes coding for the enzyme hexosaminidase or the G(M2) activator protein. Four Jacob sheep from the same farm were examined over a 3-year period for a progressive neurologic disease. Two lambs were 6-month-old intact males and 2 were 8-month-old females. Clinical findings included ataxia in all 4 limbs, proprioceptive deficits, and cortical blindness. At necropsy, the nervous system appeared grossly normal. Histologically, most neurons within the brain, spinal cord, and peripheral ganglia were enlarged, and the cytoplasm was distended by foamy to granular material that stained positively with Luxol fast blue and Sudan black B stains. Other neuropathologic findings included widespread astrocytosis, microgliosis, and scattered spheroids. Electron microscopy revealed membranous cytoplasmic bodies within the cytoplasm of neurons. Biochemical and molecular genetic studies confirmed the diagnosis of G(M2) gangliosidosis. This form of G(M2) gangliosidosis in Jacob sheep is very similar to human Tay-Sachs disease and is potentially a useful animal model.

Newly observed thalamic involvement and mutations of the HEXA gene in a Korean patient with juvenile GM2 gangliosidosis

Neuroimaging studies of patients with GM2 gangliosidosis are rare. The thalamus and basal ganglia are principally involved in patients affected by the infantile form of GM2 gangliosidosis. Unlike in the infantile form, in juvenile or adult type GM2 gangliosidosis, progressive cortical and cerebellar atrophy is the main abnormality seen on conventional magnetic resonance imaging (MRI); no basal ganglial or thalamic impairment were observed. This report is of a Korean girl with subacute onset, severe deficiency of hexosaminidase A activity and mutations (Arg137Term, Ala246Thr) of the HEXA gene. A 3.5-year-old girl who was previously in good health was evaluated for hypotonia and ataxia 3 months ago and showed progressive developmental deterioration, including cognitive decline. Serial brain MRI showed progressive overall volume decrease of the entire brain and thalamic atrophy. Fluorine-18 FDG PET scan showed severe decreased uptake in bilateral thalamus and diffuse cerebral cortex. We suggest, through our experience, that the thalamic involvement in MR imaging and FDG-PET can be observed in the juvenile form of GM2 gangliosidosis, and we suspect the association of mutations in the HEXA gene.

19 Pyrimethamine as a potential pharmacological chaperone for late-onset forms of GM2 gangliosidosis

19 Pyrimethamine as a potential pharmacological chaperone for late-onset forms of GM2 gangliosidosis

Western blotting analysis of the beta-hexosaminidase alpha- and beta-subunits in cultured fibroblasts from cases of various forms of GM2 gangliosidosis.

The GM2 gangliosidoses are a group of genetic disorders caused by the accumulation of ganglioside GM2 in neuronal cells. We examined the alpha- and beta-subunits of beta-hexosaminidases by a non-radioisotopes detecting system to evaluate whether it was a useful method for understanding of the pathophysiologies of GM2 gangliosidoses. We investigated the alpha- and beta-subunits of beta-hexosaminidases in cultured fibroblasts from cases of various forms of GM2 gangliosidosis by means of Western blotting and a chemiluminescence detection system. In a patient with infantile Tay-Sachs disease [HEXA genotype, Int5-SA(g-1-->t)/Int5-SA(g-1-->t)], the mature alpha-subunit was undetectable. In a patient with infantile Sandhoff disease (HEXB genotype, C534Y/C534Y), the mature beta-subunit was deficient. However, a small amount of the mature beta-subunit was detected in a patient with adult Sandhoff disease (HEXB genotype, R505Q(+I207V)/R505Q(+I207V)), which may have resulted in the residual enzyme activity and mild clinical course. Normal amounts of alpha- and beta-subunits were detected in a patient with GM2 activator deficiency. This method is easy and sensitive for detecting target proteins, and is useful for clarification of the pathophysiologies of GM2 gangliosidoses.

Retrospective Diagnosis of GM1 Gangliosidosis by Use of a Newborn-Screening Card

A deficiency of lysosomal β-d-galactosidase (βG; EC 3.2.1.23) is the primary defect in the three clinical forms (infantile, juvenile, and adult) of GM1 gangliosidosis and in Morquio B syndrome. Patients with the infantile form of GM1 gangliosidosis (type 1), who usually die before the age of 3 years, display the coarse face, hepatosplenomegaly, and skeletal dysplasia reminiscent of Hurler disease. Cases with later onset, described as the late infantile/juvenile form (type 2), display progressive psychomotor loss but less prominent dysmorphic changes. Extrapyramidal signs of protracted course are the major neurologic manifestations …

Structural and Functional Characterization of Streptomyces plicatus β-N-Acetylhexosaminidase by Comparative Molecular Modeling and Site-directed Mutagenesis

We have sequenced the Streptomyces plicatus beta-N-acetylhexosaminidase (SpHex) gene and identified the encoded protein as a member of family 20 glycosyl hydrolases. This family includes human beta-N-acetylhexosaminidases whose deficiency results in various forms of GM2 gangliosidosis. Based upon the x-ray structure of Serratia marcescens chitobiase (SmChb), we generated a three-dimensional model of SpHex by comparative molecular modeling. The overall structure of the enzyme is very similar to homology modeling-derived structures of human beta-N-acetylhexosaminidases, with differences being confined mainly to loop regions. From previous studies of the human enzymes, sequence alignments of family 20 enzymes, and analysis of the SmChb x-ray structure, we selected and mutated putative SpHex active site residues. Arg162 --> His mutation increased Km 40-fold and reduced Vmax 5-fold, providing the first biochemical evidence for this conserved Arg residue (Arg178 in human beta-N-acetylhexosaminidase A (HexA) and Arg349 in SmChb) as a substrate-binding residue in a family 20 enzyme, a finding consistent with our three-dimensional model of SpHex. Glu314 --> Gln reduced Vmax 296-fold, reduced Km 7-fold, and altered the pH profile, consistent with it being the catalytic acid residue as suggested by our model and other studies. Asp246 --> Asn reduced Vmax 2-fold and increased Km only 1.2-fold, suggesting that Asp246 may play a lesser role in the catalytic mechanism of this enzyme. Taken together with the x-ray structure of SmChb, these studies suggest a common catalytic mechanism for family 20 glycosyl hydrolases.

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.

Late-onset GM2 gangliosidosis: Ashkenazi Jewish family with an exon 5 mutation (Tyr180-->His) in the Hex A alpha-chain gene.

Late-onset GM2 gangliosidosis is a variant form of Tay-Sachs disease characterized by onset of symptoms and signs in adolescence or in early adult life. The deficiency of beta-hexosaminidase A (Hex A) in this form of GM2 gangliosidosis has been invariably associated with the presence of the Gly269-->Ser substitution in the alpha-chain. We found two siblings of Ashkenazi Jewish descent diagnosed with late-onset GM2 gangliosidosis who were negative for the Gly269-->Ser mutation. Analysis of the HEXA gene showed that they were compound heterozygotes for the functionally silent 4-bp insertion in exon 11, typical of the infantile form of the disease and for a novel mutation, T538-->C, resulting in the missense Tyr180-->His. Expression studies in COS-7 cells suggested that the effect of this mutation was to decrease the stability of the alpha-chain at physiologic temperatures and therefore to indirectly affect the formation of mature Hex A.

Clinical and Molecular Heterogeneity in Hereditary β-Galactosidase Deficiency

Results of a molecular analysis of GM1-gangliosidosis and galactosialidosis in our laboratory are briefly reviewed. A common single base substitution was found in adult/chronic form of GM1-gangliosidosis among heterogeneous beta-galactosidase gene mutations, and restriction site analysis was successfully performed for diagnosis of homozygotes and heterozygotes. All adult galactosialidosis patients had a common mutation at a splice junction which caused skipping of an exon of the protective protein/carboxypeptidase gene. An artificial restriction site was introduced in this case and applied to diagnosis of this disease. The heterogeneous gene mutations were compared and correlated with phenotypic manifestations in these two diseases.

Post-Partum Psychosis in Adult GM2 Gangliosidosis

Adult hexosaminidase A deficiency is a form of GM2 gangliosidosis with autosomal recessive inheritance. Only 35 cases (mostly among Ashkenazic Jews) have been reported worldwide. Symptoms include, in a third of the cases, psychosis. A 27-year-old sufferer with no prior psychiatric history, developed a post-partum psychosis, with affective and hebephrenic components, 3 days following her first delivery. She responded to lithium within 10 days of initiating treatment; the full episode lasted 1 month. We conclude that lithium is the preferred treatment for psychosis in such adult patients, especially in light of possible long-term neurological deterioration caused by phenothiazines. Ashkenazic Jews with atypical neurological syndromes presenting with psychosis should be tested for hexosaminidase A deficiency.

GM2 gangliosidosis with a motor neuron disease phenotype: clinical heterogeneity of hexosaminidase deficiency disease.

The existence of families in which amyotrophic lateral sclerosis (ALS) is present, transmitted by an autosomal dominant trait, is well-known. In contrast with these more common cases, only a few familial cases occur with a pattern suggesting autosomal recessive inheritance. These genetic cases have recently stimulated research into the genetic dismetabolic conditions that could cause a phenotype similar to ALS or motor neuron diseases. In such families with atypical ALS cases, several typical Tay Sachs1 disease patients have been found[l]. In a screening program for Tay Sachs’ disease, several cases with a motor neuron phenotype and an absence of hexosaminidase activity were found [2]. The same enzyme defect has been reported in young patients with a phenotype similar to juvenile muscular atrophy, Kugelberg-Welander phenotype [3], confirming that primary pathological changes of anterior horn cells can be possible in several cases with juvenile, infantile and adult forms of GM2 gangliosidosis. These forms are clinically characterized by a slow evolution and biochemically by an incomplete absence of hexosaminidase A or B or both.

GM1 Gangliosidosis, type 2: ocular clinicopathologic correlation

The clinical and pathological manifestations of a case of juvenile GM1 gangliosidosis are presented and the pathological findings compared with those previously reported for GM1 gangliosidosis in man and in animal models. The most striking finding in the present case was the marked degeneration of the retinal ganglion cell and nerve fiber layers. Although such extensive ganglion cell loss was not observed in any of the other cases reviewed, the presence of multimembranous inclusion bodies in retinal ganglion cells strongly suggests that the pathological process was similar in all cases. Much remains to be learned about the function of gangliosides in the healthy retina and about the pathophysiological consequences of deranged ganglioside metabolism. The many parallels, including those observed in pathological studies, between the human and animal forms of GM1 gangliosidosis allow an optimistic appraisal of the value of further research using the animal models.

Processing of human beta-galactosidase in GM1-gangliosidosis and Morquio B syndrome.

The nature of the molecular defect resulting in the beta-galactosidase deficiency in different forms of GM1-gangliosidosis and mucopolysaccharidosis IV B (Morquio B syndrome) was investigated. Normal and mutant cultured skin fibroblasts were labeled in vivo with [3H]leucine and immunoprecipitation studies with human anti-beta-galactosidase antiserum were performed, followed by polyacrylamide gel electrophoresis and fluorography. In Morquio B syndrome, the mutation does not interfere with the normal processing and intralysosomal aggregation of beta-galactosidase. In cells from infantile and adult GM1-gangliosidosis, 85-kDa precursor beta-galactosidase was found to be synthesized normally but more than 90% of the enzyme was subsequently degraded at one of the early steps in posttranslational processing. The residual 5-10% beta-galactosidase activity in adult GM1-gangliosidosis is 64-kDa mature lysosomal enzyme with normal catalytic properties but with a reduced ability of the monomeric form to aggregate into high molecular weight multimers. Knowledge of the exact nature of the molecular defect underlying beta-galactosidase deficiency in man may lead to a better understanding of the clinical and pathological heterogeneity among patients with different types of GM1-gangliosidosis and Morquio B syndrome.

Substrate specificity of hexosaminidase A isolated from the liver of a patient with a rare form (AB variant) of infantile GM2 gangliosidosis and control tissues.

An inheritable deficiency of hexosaminidase A and A and B causes neuronal storage of glycolipids in patients with the B variant (Tay-Sachs disease) and 0 variant form, respectively, of infantile GM2 gangliosidosis. The same glycolipids, the GM2 ganglioside and its GA2 asialo-derivative, accumulate also in the neural tissues of patients with the AB variant form of the disease (1). In this form, however, a deficient activity of hexosaminidase A could not be demonstrated using synthetic substrates. In order to test the possibility of a mutant hexosaminidase A occurring in patients with this form of GM2 gangliosidosis, the enzyme obtained from the liver of an autopsy case of this disease variant was purified to homogeneity and characterized. Purification was achieved by affinity chromatography using a newly synthesized selective adsorbent ((6-Aminohexyl)-1-thio-2-acetamido-2-deoxy-ß-D-galactopyranoside) as substrate analog (2). The ligand has been shown to possess a competitive inhibitory effect (Ki = 0.17 mM) upon the enzyme under study.

Storage and excretion of oligosaccharides and glycopeptides in the gangliosidoses.

Electron microscopical studies of visceral tissues from the infantile form of GM1-gangliosidosis (Type I or generalized gangliosidosis) show extensive cytoplasmic vacuolation of parenchymal cells, histiocytes, fibrocytes and lymphocytes (9,23–25, 29,33,36,44). Indeed, in the liver, the majority of the hepatocytes are packed with membrane-limited vacuoles filled with highly water-soluble, α-amylase-resistant, PAS-positive material. Similar morphological features are also seen in an affected fetus at 17 weeks of gestation with in addition intense vacuolation of the syncytiotrophoblasts of the placenta (16,28). Vacuolation of hepatocytes is much less marked in the Type II late infantile or juvenile form of of-gangliosidosis (9,11,27). It was recognized early in the descriptions of this disease that the material stored in the vacuoles was unlikely to be GM1-ganglioside since the ul trastructural features were quite different from the neuronal membranous cytoplasmic bodies characteristic of ganglioside storage. Earlier chemical studies of not too rigorous a nature established that the liver from Type I GM1-gangliosidosis contained excessive amounts of polysaccharides rich in galactose and N-acetylglucosamine and fractions containing some mannose were also recognized (5,32–34,44).

Glycoproteins in brain tissue of the O-variant of GM2 gangliosidosis.

Abstract— The dialysableglycopeptide preparation recovered from the glycoproteins in cerebral gray matter of a case of the O‐variant form of GM2 gangliosidosis contained four fold more N‐acetylglucosamine and mannose than a similar preparation from normal gray matter. In the O‐variant form of GM2 gangliosidosis, the enzymes β‐N‐acetylhexosaminidases A and B are missing. A three‐ and four‐fold elevation, respectively, of N‐acetylglucosamine and mannose in the dialysable glycopeptide preparation from a case of Tay‐Sachs disease (B‐variant form of GM2 gangliosidosis) was noted. The B‐variant lacks hexosaminidase A but has ample supplies of hexosaminidase B. The brain level of glycosaminoglycans was not affected in the O‐ and B‐variant forms of GM2 gangliosidosis.