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[Lysosome disease--Sandhoff disease].

Lysosomal beta-hexosaminidase occurs as two major isozymes hexosaminidase A and B. The alpha subunit is encoded by the HEXA gene and the subunit by HEXB gene. Defects in the beta subunit lead to Sandhoff disease. Patients with the defect lack the activity or formation of both hexosaminidase A and B. The disorders are classified according to the age of onset, as infantile, juvenile and adult form. Recent molecular genetic analysis has revealed a 50 kb deletion, 16 kb Alu type deletion, and compound heterozygous with other mutations. In the juvenile or adult type of the disease, point mutation of the HEXB gene, creating a new 3' splice acceptor site. The correlation of the clinical phenotype and the gene abnormalities is discussed.

Adolescent↗

Phospholipid synthesis is decreased in neuronal tissue in a mouse model of Sandhoff disease.

Sandhoff disease is a progressive neurodegenerative disorder caused by mutations in the HEXB gene which encodes for the beta-subunit of beta-hexosaminidase A and B, resulting in ganglioside GM(2) accumulation in the brain. We now demonstrate that phospholipid metabolism is altered in both cultured neurons and in brain tissue from a mouse model of Sandhoff disease, the Hexb-/- mouse. Metabolic labelling using [methyl-(14)C]choline and l-[3-(3)H]serine demonstrated reduced incorporation of [methyl-(14)C]choline into phospholipids in brain tissue but not in liver or spleen. Phospholipid mass was also reduced in brain. The activities of CTP : phosphocholine cytidylyltransferase (CCT) and phosphatidylserine synthase were also reduced in brain tissue from Hexb-/- mice, probably because of post-translational modification as no changes were observed in levels of enzyme expression. The relevance of these findings to Sandhoff disease in human patients is strengthened by observations made over 30 years ago on autopsy tissue of Tay Sachs and Sandhoff disease patients, in which reduced phospholipid levels were observed. We suggest that changes in phospholipid metabolism are not simply because of loss of neuronal tissue as a result of degeneration but rather may cause degeneration, and we discuss the possible effects that changes in phospholipid metabolism could play in the neuropathophysiology of Sandhoff disease.

Animals↗

A case refort of Sandhoff disease.

Sandhoff disease is a rare autosomal recessive metabolic disease presenting bilateral optic atrophy and a cherry red spot in the macula. This case report presents the characteristics of a patient with Sandhoff disease as assessed by ophthalmic, neuroimaging, and laboratory procedures. Ophthalmologic examination revealed that the patient could not fixate her eyes on objects nor follow moving targets. A pale optic disc and a cherry red spot in the macula were seen in both eyes. Low signal intensity at the thalamus and high signal intensity at the cerebral white matter were noted in a T2-weighted brain MR image. A lysosomal enzyme assay using fibroblasts showed the marked reduction of both total beta-hexosaminidases, A and B. Based on the above clinical manifestations and laboratory findings, we diagnosed the patient as having Sandhoff disease.

Atrophy↗

Lysosomal storage results in impaired survival but normal neurite outgrowth in dorsal root ganglion neurones from a mouse model of Sandhoff disease.

Sandhoff disease is a heritable lysosomal storage disease resulting from impaired degradation of GM2 ganglioside and related substrates. A mouse model of Sandhoff disease created by gene targeting displays progressive neurological manifestations, similar to patients with the disease. In the present in vivo and in vitro studies, we examined morphological and functional abnormalities of dorsal root ganglion (DRG) neurones in Sandhoff disease mice at an asymptomatic stage (approximately 1 month of age). Light microscopic studies with Nissl staining and immunocytochemistry suggested extensive intracytoplasmic storage of GM2 ganglioside in the Sandhoff mouse DRG neurones. These findings were consistent with the results of electron microscopy, in which a huge number of pleomorphic inclusion bodies immunoreactive for GM2 ganglioside were present in the cytoplasm of the neurones. The inclusion bodies were also identified in satellite cells and Schwann cells in the Sandhoff mouse DRG. The survival ratios of DRG neurones after 1, 2, 4 and 6 days in culture were significantly lower in the Sandhoff mice than in the age-matched heterozygous mice. The ratio of neurite-bearing cells on poly-l-lysine-coated dishes after 2 days in culture was also lower by approximately 10% in the Sandhoff mice compared to the heterozygotes, but additional coating of laminin onto poly-l-lysine dramatically enhanced the neurite extension from the neurones in both groups of mice. These results indicate that accumulation of GM2 ganglioside in DRG neurones impairs the capability of the neurones to survive in vitro, although viable neurones from the Sandhoff mice in culture can regenerate neurites nearly as well as unaffected neurones.

Animals↗

Thalamic hyperdensity--is it a diagnostic marker for Sandhoff disease?

Sandhoff disease, also known as GM2-gangliosidoses variant 0, is caused by the deficient activity of both hexosaminidase A and hexosaminidase B. We report a 15-month-old boy diagnosed with Sandhoff disease by demonstrating the enzyme deficiency. The interesting finding was bilateral thalamic hyperdensity on the CT scan. The hyperdensity in all previously published cases was homogeneous and symmetric and limited to the thalamus; the cause still remains unknown. We suggest that the finding of dense thalami may be useful as a specific diagnostic criterion for the GM2-gangliosidoses and especially for Sandhoff disease.

Brain↗

Improved outcome of N-butyldeoxygalactonojirimycin-mediated substrate reduction therapy in a mouse model of Sandhoff disease.

Sandhoff disease is a severe neurodegenerative glycosphingolipid (GSL) lysosomal storage disorder, currently without treatment options. One therapeutic approach under investigation is substrate reduction therapy (SRT). By partially inhibiting GSL biosynthesis, the impaired rate of GSL catabolism is balanced by a slower rate of influx of GSLs into the lysosome. In a previous study, we reported the beneficial effects of treating Sandhoff disease mice with the glucose analogue N-butyldeoxynojirimycin (NB-DNJ), a compound that inhibits the first step of GSL biosynthesis catalysed by the ceramide specific glucosyltransferase. NB-DNJ, however, exhibits adverse effects at high doses such as weight loss and GI tract distress (due to glucosidase inhibition). This might limit the therapeutic potential of NB-DNJ for treating diseases affecting the CNS where high dose therapy may be required to achieve therapeutic levels of the drug in the brain. In the present study, a more selective compound, the galactose analogue N-butyldeoxygalactonojirimycin (NB-DGJ), was evaluated in the Sandhoff disease mouse model. Treatment with NB-DGJ showed greater therapeutic efficacy than NB-DNJ with no detectable side effects. The ability to escalate the dose of NB-DGJ, leading to extended life expectancy and increased delay in symptom onset, demonstrates the greater therapeutic potential of NB-DGJ for the treatment of the human gangliosidoses.

1-Deoxynojirimycin↗

Neuroimaging findings of four patients with Sandhoff disease.

Sandhoff disease is a severe form of GM2 gangliosidosis that is caused by the deficiency of both hexosaminidase A and B. Startle reaction, hypotonia, psychomotor retardation, and blindness are the main clinical features. Presented are computed tomography and magnetic resonance imaging findings of four patients with Sandhoff disease diagnosed by enzymatic analyses. Bilateral homogeneous thalamic hyperdensity was evident on computed tomography. Magnetic resonance imaging scans revealed mild cortical atrophy, a thin corpus callosum, and abnormal signal intensities in the caudate nucleus, globus pallidum, putamen, cerebellum, and brainstem. No correlation was evident between the severity of the central nervous system imaging findings and the clinical pictures. In this article the neuroimaging findings of four patients with Sandhoff disease are discussed.

Adolescent↗

Plasmid-based gene transfer ameliorates visceral storage in a mouse model of Sandhoff disease.

Sandhoff disease is a severe neurodegenerative disorder with visceral involvement caused by mutations in the HEXB gene coding for the beta subunit of the lysosomal hexosaminidases A and B. HEXB mutations result in the accumulation of undegraded substrates such as GM2 and GA2 in lysosomes. We evaluated the efficacy of cationic liposome-mediated plasmid gene therapy using the Sandhoff disease mouse, an animal model of a human lysosomal storage disease. The mice received a single intravenous injection of two plasmids, encoding the human alpha and beta subunits of hexosaminidase cDNAs. As a result, 10-35% of normal levels of hexosaminidase expression, theoretically therapeutic levels, were achieved in most visceral organs, but not in the brain, 3 days after injection with decreased levels by day 7. Histochemical staining confirmed widespread enzyme activity in visceral organs. Both GA2 and GM2 were reduced by almost 10% and 50%, respectively, on day 3, and by 60% and 70% on day 7 compared with untreated age-matched Sandhoff disease mice. Consistent with the biochemical results, a reduction in GM2 was observed in liver cells histologically as well. These initial findings support further development of the plasmid gene therapy against lysosomal diseases with visceral pathology.

Animals↗

Structure and distribution of an Alu-type deletion mutation in Sandhoff disease.

Sandhoff disease is a recessively inherited lysosomal storage disease resulting from a deficiency of beta-hexosaminidase activity. The enzyme occurs in two major forms, beta-hexosaminidase A, composed of an alpha- and beta-subunit and beta-hexosaminidase B, composed of two beta-subunits. Both isozyme activities are deficient in Sandhoff disease, owing to mutations of the HEXB gene encoding the common beta-subunit. We have cloned and fully characterized a deletion at the HEXB gene from fibroblasts of a patient with the infantile form of Sandhoff disease. The deletion removes approximately 16 kb of DNA including the HEXB promoter, exons 1-5 and part of intron 5. It most likely arose from recombination between two Alu sequences, with the breakpoints occurring at the midpoint between the left and right arms in each case and regenerating an intact Alu element in the deletion sequence. The deletion allele accounts for 27% of the Sandhoff mutant alleles we analyzed. Two cell lines were shown to be homozygous for the deletion and both had the infantile form of the disease. Four additional patients were compound heterozygotes with other mutations, all of whom displayed a different clinical phenotype. Finally, the mutant allele was present in different ethnic backgrounds, suggesting that it may have been subject to genetic drift.

Base Sequence↗

Development of infertility at young adult age in a mouse model of human Sandhoff disease.

Sandhoff disease is a human lysosomal storage disease. In a knockout mouse model of Sandhoff disease, which lacks the beta-subunit of beta-hexosaminidase A (Hex A, alphabeta subunits) and B (Hex B, betabeta subunits), the mutant homozygous mice (Hexb(-/-)) are healthy until 15 weeks of age when they develop neurodegenerative symptoms. This study was designed to analyse the fertility profile of male and female Hexb(-/-) mice. Mating behaviour of Hexb(-/-) mice was assessed at different ages. The ovarian function of Hexb(-/-) females was determined by superovulation studies. The quality of spermatozoa and ova was assessed by an in vitro fertilization (IVF) procedure. Hexb(-/-) mice were fertile at a young age. Males were fertile up to the age of 69.3 +/- 6.3 days (mean +/- SD) and females were fertile up to the age of 56-63 days. Since both the Hexb (-/-) sexes showed fertility, the results indicate that Hex A and Hex B (major isozymes of beta-hexosaminidase) may not be required for sperm-ovum interactions, in contrast to the widely accepted belief. On the other hand, young adult Hexb(-/-) males showed a reduction in mating behaviour at the age of 84.8 +/- 2.2 days and an absence of mating behaviour at 94.2 +/- 2.0 days. Spermatozoa from Hexb(-/-) mice (aged 109.2 +/- 1.8 days) showed a lower IVF rate. Among Hexb (-/-) females aged 85.6 +/- 2.1 days, no mice became pregnant although they were positive for a vaginal plug when caged with fertile males. The number of ova recovered from Hexb(-/-) females (aged 111.0 +/- 3.1 days) and the IVF rate of ova were lower than those of controls. In conclusion, Hex A and Hex B may not be required for sperm-ovum interactions. Mice lacking Hex A and Hex B activities develop infertility at a young adult age in an age-dependent manner.

Aging↗

Novel splice site mutation at IVS8 nt 5 of HEXB responsible for a Greek-Cypriot case of Sandhoff disease.

Sandhoff disease is caused by abnormalities in HEXB gene encoding the beta-subunit of beta-hexosaminidase. In this study, we analyzed the HEXB gene of a Sandhoff carrier in the Greek-Cypriot community. A G to C transversion was identified in one allele of her HEXB gene at position 5 of the 5'-splice site of intron 8 (IVS8 nt5). One of 13 cDNA clones derived from her lymphocyte HEXB mRNA lacked the last four nucleotides "GTTG" of exon 8, which created a premature termination codon at 11 codons downstream. In vivo transcription of the mutant HEXB gene fragment in CHO cells resulted in deletion of the "GTTG." The mutation has not been found in 40 DNA samples from anonymous donors, indicating that this is not a polymorphism in the Cypriot population. These results clearly indicate that the splice site mutation at IVS8 nt5 is responsible for this case of Sandhoff disease.

Bacterial Proteins↗

Reduced rates of axonal and dendritic growth in embryonic hippocampal neurones cultured from a mouse model of Sandhoff disease.

Sandhoff disease is a lysosomal storage disease in which ganglioside GM2 accumulates because of a defective beta-subunit of beta-hexosaminidase. This disease is characterized by neurological manifestations, although the pathogenic mechanisms leading from GM2 accumulation to neuropathology are largely unknown. We now examine the viability, development and rates of neurite growth of embryonic hippocampal neurones cultured from a mouse model of Sandhoff disease, the Hexb-/- mouse. GM2 was detected by metabolic labelling at low levels in wild type (Hexb+/+) neurones, and increased by approximately three-fold in Hexb-/- neurones. Hexb-/- hippocampal neurones were as viable as their wild type counterparts and, moreover, their developmental programme was unaltered because the formation of axons and of the minor processes which eventually become dendrites was similar in Hexb-/- and Hexb+/+ neurones. In contrast, once formed, a striking difference in the rate of axonal and minor process growth was observed, with changes becoming apparent after 3 days in culture and highly significant after 5 days in culture. Analysis of various parameters of axonal growth suggested that a key reason for the decreased rate of axonal growth was because of a decrease in the formation of collateral axonal branches, the major mechanism by which hippocampal axons elongate in culture. Thus, although the developmental programme with respect to axon and minor process formation and the viability of hippocampal neurones are unaltered, a significant decrease occurs in the rate of axonal and minor process growth in Hexb-/- neurones. These results appear to be in contrast to dorsal root ganglion neurones cultured from 1-month-old Sandhoff mice, in which cell survival is impaired but normal outgrowth of neurones occurs. The possible reasons for these differences are discussed.

Animals↗

MRS reveals additional hexose N-acetyl resonances in the brain of a mouse model for Sandhoff disease.

Sandhoff disease, one of several related lysosomal storage disorders, results from the build up of N-acetyl-containing glycosphingolipids in the brain and is caused by mutations in the genes encoding the hexosaminidase beta-subunit. Affected individuals undergo progressive neurodegeneration in response to the glycosphingolipid storage. (1)H magnetic resonance spectra of perchloric acid extracts of Sandhoff mouse brain exhibited several resonances ca 2.07 ppm that were not present in the corresponding spectra from extracts of wild-type mouse brain. High-performance liquid chromatography and mass spectrometry of the Sandhoff extracts post-MRS identified the presence of N-acetylhexosamine-containing oligosaccharides, which are the likely cause of the additional MRS resonances. MRS of intact brain tissue with magic angle spinning also showed additional resonances at ca 2.07 ppm in the Sandhoff case. These resonances appeared to increase with disease progression and probably arise, for the most part, from the stored glycosphingolipids, which are absent in the aqueous extracts. Hence in vivo MRS may be a useful tool for detecting early-stage Sandhoff disease and response to treatment.

Animals↗

Impact of premature stop codons on mRNA levels in infantile Sandhoff disease.

Sandhoff disease is an autosomal recessive lysosomal storage disease resulting from mutations of the HEXB gene encoding the beta subunit of beta-hexosaminidase A. Fibroblast lines from four patients with the infantile form of the disease were investigated for mutations by single strand conformation polymorphism analysis and direct sequencing of PCR products. Two of the cell lines were homozygous for a common, 16 kb deletion of the 5' end of HEXB gene. The two other cell lines contained the 16 kb deletion along with a second mutant allele generating a stop codon: in one case a nonsense mutation, C850-->T, which generated a stop codon at codon 284; and in the other, a single base deletion, delta T1344, which generated a stop codon at codon 451. One additional cell line investigated was a compound heterozygote for two frameshift mutations, delta G774 in exon 7 and delta AG1305-1306 in exon 11 (McInnes et al. 1992, Biochim. Biophys. Acta 1138: 315-317). Stop codons were generated in this cell line at codons 274 and 454, respectively. We took advantage of these genotypes to investigate the steady-state level of mRNA produced by cells containing stop codons using a competitive polymerase chain reaction technique. The mRNA levels were, as percent of normal per single gene dose: for the stop codon at codon 451, 30%; for those at codons 274 and 454, combined percentage of 1.7%; and at codon 284, 0.8%. These studies demonstrate a dramatic difference in the steady-state level of Hex beta mRNA in the cell lines with stop codons in close proximity to each other (codons 451 vs 454).(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

Sandhoff disease heterozygote detection: a component of population screening for Tay-Sachs disease carriers. II. Sandhoff disease gene frequencies in American Jewish and non-Jewish populations.

Carrier frequencies for the allele(s) causing Sandhoff disease have been estimated for the U.S. Jewish and non-Jewish populations. The estimates have been made directly, with data from 22,043 Jewish and 32,342 non-Jewish individuals measured for total serum hexosaminidase activity and the heat-labile fraction. These values have been shown to identify potential carriers of the Sandhoff allele(s) with 95% sensitivity. Subsequent leukocyte assays of total hexosaminidase activity and the heat-labile fraction in those identified in serum tests have been shown to provide a much finer discrimination between those who carry the allele(s) and those who do not. Results from such assays were used to generate these carrier frequency estimates. Carrier frequency estimates have also been made indirectly from Sandhoff disease incidence data collected during the period 1979-84. These estimates are in agreement with data for the Jewish population under analysis, but in the non-Jewish population the estimate derived from data on screened individuals is greater than the estimate derived from incidence figures. The possible causes for such a difference are discussed. In a study of non-Jewish individuals each of whose grandparents derives from a single country of origin, the distribution of countries among Sandhoff disease carriers differs significantly from that in the non-Jewish sample under analysis, indicating possible ethnic groups with increased or decreased carrier frequencies. These analyses suggest an increased Sandhoff disease carrier frequency among Mexican and Central-American populations and a decreased carrier frequency among non-Jewish German populations.

Gene Frequency↗

Bone marrow transplantation prolongs life span and ameliorates neurologic manifestations in Sandhoff disease mice.

The GM2 gangliosidoses are a group of severe, neurodegenerative conditions that include Tay-Sachs disease, Sandhoff disease, and the GM2 activator deficiency. Bone marrow transplantation (BMT) was examined as a potential treatment for these disorders using a Sandhoff disease mouse model. BMT extended the life span of these mice from approximately 4.5 mo to up to 8 mo and slowed their neurologic deterioration. BMT also corrected biochemical deficiencies in somatic tissues as indicated by decreased excretion of urinary oligosaccharides, and lower glycolipid storage and increased levels of beta-hexosaminidase activity in visceral organs. Even with neurologic improvement, neither clear reduction of brain glycolipid storage nor improvement in neuronal pathology could be detected, suggesting a complex pathogenic mechanism. Histological analysis revealed beta-hexosaminidase-positive cells in the central nervous system and visceral organs with a concomitant reduction of colloidal iron-positive macrophages. These results may be important for the design of treatment approaches for the GM2 gangliosidoses.

Animals↗

Composition of gangliosides and neutral glycosphingolipids of brain in classical Tay-Sachs and Sandhoff disease: more lyso-GM2 in Sandhoff disease?

The ganglioside composition of the brain from an individual with classical Tay-Sachs disease and from an individual with Sandhoff disease was examined using our new quantitative methods for ganglioside content determination and compared with that of age-matched control brains. The concentration of GM2 was found to be 12.2 and 13.0 mumol/g of fresh tissue in Tay-Sachs disease and in Sandhoff disease cerebral gray matter, respectively. GM2 was 86 and 87% respectively, of total gangliosides. The concentration of GM1 and, in particular, GM3 ganglioside was also found to be increased, whereas the concentration of the major di- and trisialogangliosides (GD1a, GD1b, and GT1b) had diminished markedly. There was no significant increase in level of any other ganglioside than lyso-GM2. Its concentration was 12 and 16 nmol/g in cerebral gray matter of two Tay-Sachs disease brains and 43 nmol/g in Sandhoff disease brain. The Sandhoff disease brain also differed from the classical Tay-Sachs disease brain by having a much higher concentration of gangliotriaosylceramide and globotetraosylceramide. The structures of relevant gangliosides and neutral glycolipids were established by fast atom bombardment-mass spectrometry and permethylation studies.

Brain Chemistry↗