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Mahdieh N, Mikaeeli S, Tavasoli AR, Rezaei Z, Maleki M, Rabbani B. Genotype, phenotype and in silico pathogenicity analysis of HEXB mutations: Panel based sequencing for differential diagnosis of gangliosidosis. Clin Neurol Neurosurg 2018; 167:43-53. [PMID: 29448188 DOI: 10.1016/j.clineuro.2018.02.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 01/31/2018] [Accepted: 02/05/2018] [Indexed: 10/18/2022]
Abstract
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.
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Affiliation(s)
- Nejat Mahdieh
- Genetic Research Center, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran.
| | - Sahar Mikaeeli
- Genetic Research Center, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
| | - Ali Reza Tavasoli
- Children's Hospital Center, Pediatric Center of Excellence, Tehran University of Medical Center, Tehran, Iran; Growth and Development Research, Tehran University of Medical Sciences, Tehran, Iran
| | - Zahra Rezaei
- Children's Hospital Center, Pediatric Center of Excellence, Tehran University of Medical Center, Tehran, Iran
| | - Majid Maleki
- Genetic Research Center, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
| | - Bahareh Rabbani
- Genetic Research Center, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran; Growth and Development Research, Tehran University of Medical Sciences, Tehran, Iran.
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Ohno K, Takeda JI, Masuda A. Rules and tools to predict the splicing effects of exonic and intronic mutations. WILEY INTERDISCIPLINARY REVIEWS-RNA 2017; 9. [DOI: 10.1002/wrna.1451] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 08/23/2017] [Accepted: 08/24/2017] [Indexed: 12/14/2022]
Affiliation(s)
- Kinji Ohno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer; Nagoya University Graduate School of Medicine; Nagoya Japan
| | - Jun-ichi Takeda
- Division of Neurogenetics, Center for Neurological Diseases and Cancer; Nagoya University Graduate School of Medicine; Nagoya Japan
| | - Akio Masuda
- Division of Neurogenetics, Center for Neurological Diseases and Cancer; Nagoya University Graduate School of Medicine; Nagoya Japan
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Original tandem duplication in FXIIIA gene with splicing site modification and four amino acids insertion causes factor XIII deficiency. Blood Coagul Fibrinolysis 2017; 28:237-243. [PMID: 27427785 DOI: 10.1097/mbc.0000000000000587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
: Recessive mutations of F13A gene are reported to be responsible of FXIIIA subunit deficiency (FXIIIA). In all, some intronic nucleotide changes identified in this gene were investigated by in-silico analysis and occasionally supported by experimental data or reported in some cases as a polymorphism. To determine the molecular defects responsible of congenital factor XIII deficiency in Libyan patient, molecular analysis was performed by direct DNA sequencing of the coding regions and splice junctions of the FXIIIA subunit gene (F13A). A splicing minigene assay was used to study the effect of this mutation. Bioinformatics exploration was fulfilled to conceive consequences on protein. A 12-bp duplication straddling the border of intron 9 and exon 10 leads to two 3' acceptor splice sites, resulting in silencing of the downstream wild 3' splice site. It caused an in-frame insertion of 12 nucleotides into mRNA and four amino acids into protein. Bioinformatic analysis predicts that the insertion of four amino acids affects the site 3 of calcium binding site, which disturbs the smooth function of the FXIIIA peptide causing the factor XIII deficiency. This study showed that a small duplication seems to weaken the original 3' splice site and enhance the activation of a new splice site responsible for an alternative splicing. It would be interesting to examine the underlying molecular mechanism involved in this rearrangement.
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Olkhovych NV, Gorovenko NG. Determination of frequencies of alleles, associated with the pseudodeficiency of lysosomal hydrolases, in population of Ukraine. UKRAINIAN BIOCHEMICAL JOURNAL 2016; 88:96-106. [PMID: 29235819 DOI: 10.15407/ubj88.05.096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The pseudodeficiency of lysosomal hydrolases described as a significant reduction in enzyme activity in vitro in clinically healthy individuals, can lead to diagnostic errors in the process of biochemical analysis of lysosomal storage disease in case of its combination with pathology of another origin. Pseudodeficiency is mostly caused by some non-pathogenic changes in the corresponding gene. These changes lead to the in vitro lability of the enzyme molecule, whereas in vivo the enzyme retains its functional activity. To assess the prevalence of the most common lysosomal hydrolases pseudodeficiency alleles in Ukraine, we have determined the frequency of alleles c.1055A>G and c.* 96A>G in the ARSA gene, substitutions c.739C>T (R247W) and c.745C>T (R249W) in the HEXA gene, c.1726G>A (G576S) and c.2065G>A (E689K) in the GAA gene, c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene in a group of 117 healthy individuals from different regions of the country and 14 heterozygous carriers of pathogenic mutations in the HEXA gene (parents of children with confirmed diagnosis of Tay-Sachs disease). The total frequency of haplotypes, associated with arylsulfatase A pseudodeficiency, in healthy people in Ukraine (c.1055G/c.*96G and c.1055G/c.*96A haplotypes) was 10.3%. The frequency of c.739C>T (R247W) allele, associated with hexosaminidase A pseudodeficiency, among Tay-Sachs carriers from Ukraine was 7.1%. The total frequency of α-glucosidase pseudodeficiency haplotypes in healthy individuals in Ukraine (c.1726A/c.2065A and c.1726G/c.2065A haplotypes) was 2.6%. No person among examined individuals with the substitution c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene was found. The differential diagnostics of lysosomal storage diseases requires obligatory determination of the presence of the pseudodeficiency alleles, particularly the ones with high incidence in the total population. Ignoring phenomenon of pseudodeficiency may lead to serious diagnostic errors.
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Gaignard P, Fagart J, Niemir N, Puech JP, Azouguene E, Dussau J, Caillaud C. Characterization of seven novel mutations on the HEXB gene in French Sandhoff patients. Gene 2012; 512:521-6. [PMID: 23046579 DOI: 10.1016/j.gene.2012.09.124] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Accepted: 09/29/2012] [Indexed: 01/22/2023]
Abstract
Sandhoff disease (SD) is an autosomal recessive lysosomal storage disease caused by mutations in the HEXB gene encoding the beta subunit of hexosaminidases A and B, two enzymes involved in GM2 ganglioside degradation. Eleven French Sandhoff patients with infantile or juvenile forms of the disease were completely characterized using sequencing of the HEXB gene. A specific procedure was developed to facilitate the detection of the common 5'-end 16kb deletion which was frequent (36% of the alleles) in our study. Eleven other disease-causing mutations were found, among which four have previously been reported (c.850C>T, c.793T>G, c.115del and c.800_817del). Seven mutations were completely novel and were analyzed using molecular modelling. Two deletions (c.176del and c.1058_1060del), a duplication (c.1485_1487dup) and a nonsense mutation (c.552T>G) were predicted to strongly alter the enzyme spatial organization. The splice mutation c.558+5G>A affecting the intron 4 consensus splice site led to a skipping of exon 4 and to a truncated protein (p.191X). Two missense mutations were found among the patients studied. The c.448A>C mutation was probably a severe mutation as it was present in association with the known c.793T>G in an infantile form of Sandhoff disease and as it significantly modified the N-terminal domain structure of the protein. The c.171G>C mutation resulting in a p.W57C amino acid substitution in the N-terminal region is probably less drastic than the other abnormalities as it was present in a juvenile patient in association with the c.176del. Finally, this study reports a rapid detection of the Sandhoff disease-causing alleles facilitating genetic counselling and prenatal diagnosis in at-risk families.
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Affiliation(s)
- Pauline Gaignard
- Service de Biochimie et Génétique Moléculaire, Groupe Hospitalier Cochin - Broca - Hotel Dieu, Assistance Publique - Hôpitaux de Paris, Paris, France
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Maegawa GHB, Stockley T, Tropak M, Banwell B, Blaser S, Kok F, Giugliani R, Mahuran D, Clarke JTR. The natural history of juvenile or subacute GM2 gangliosidosis: 21 new cases and literature review of 134 previously reported. Pediatrics 2006; 118:e1550-62. [PMID: 17015493 PMCID: PMC2910078 DOI: 10.1542/peds.2006-0588] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
OBJECTIVE Juvenile GM2 gangliosidosis is a group of inherited neurodegenerative diseases caused by deficiency of lysosomal beta-hexosaminidase resulting in GM2 ganglioside accumulation in brain. The purpose of this study was to delineate the natural history of the condition and identify genotype-phenotype correlations that might be helpful in predicting the course of the disease in individual patients. METHODS A cohort of 21 patients with juvenile GM2 gangliosidosis, 15 with the Tay-Sachs variant and 6 with the Sandhoff variant, was studied prospectively in 2 centers. Our experience was compared with previously published reports on 134 patients. Information about clinical features, beta-hexosaminidase enzyme activity, and mutation analysis was collected. RESULTS In our cohort of patients, the mean (+/-SD) age of onset of symptoms was 5.3 +/- 4.1 years, with a mean follow-up time of 8.4 years. The most common symptoms at onset were gait disturbances (66.7%), incoordination (52.4%), speech problems (28.6%), and developmental delay (28.6%). The age of onset of gait disturbances was 7.1 +/- 5.6 years. The mean time for progression to becoming wheelchair-bound was 6.2 +/- 5.5 years. The mean age of onset of speech problems was 7.0 +/- 5.6 years, with a mean time of progression to anarthria of 5.6 +/- 5.3 years. Muscle wasting (10.6 +/- 7.4 years), proximal weakness (11.1 +/- 7.7 years), and incontinence of sphincters (14.6 +/- 9.7 years) appeared later in the course of the disease. Psychiatric disturbances and neuropathy were more prevalent in patients with the Sandhoff variant than in those with the Tay-Sachs variant. However, dysphagia, sphincter incontinence, and sleep problems occurred earlier in those with the Tay-Sachs variant. Cerebellar atrophy was the most common finding on brain MRI (52.9%). The median survival time among the studied and reviewed patients was 14.5 years. The genotype-phenotype correlation revealed that in patients with the Tay-Sachs variant, the presence of R178H and R499H mutations was predictive of an early onset and rapidly progressive course. The presence of either G269S or W474C mutations was associated with a later onset of symptoms along with a more slowly progressive disease course. CONCLUSIONS Juvenile GM2 gangliosidosis is clinically heterogeneous, not only in terms of age of onset and clinical features but also with regard to the course of the disease. In general, the earlier the onset of symptoms, the more rapidly the disease progresses. The Tay-Sachs and Sandhoff variants differed somewhat in the frequency of specific clinical characteristics. Speech deterioration progressed more rapidly than gait abnormalities in both the Tay-Sachs variant and Sandhoff variant groups. Among patients with the Tay-Sachs variant, the HEXA genotype showed a significant correlation with the clinical course.
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Affiliation(s)
- Gustavo H. B. Maegawa
- Division of Clinical and Metabolic Genetics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
- Research Institute, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
- Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada
| | - Tracy Stockley
- Department of Paediatrics, Paediatric Laboratory Medicine, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Michael Tropak
- Research Institute, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Brenda Banwell
- Division of Neurology, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Susan Blaser
- Department of Paediatrics, Diagnostic Imaging, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Fernando Kok
- Centro do Genoma Humano, University of Sao Paulo, Sao Paulo, Brazil
| | - Roberto Giugliani
- Medical Genetics Service, Hospital de Clinicas de Porto Alegre, Porto Alegre, Brazil
| | - Don Mahuran
- Research Institute, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Joe T. R. Clarke
- Division of Clinical and Metabolic Genetics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
- Research Institute, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
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Sawkar AR, Adamski-Werner SL, Cheng WC, Wong CH, Beutler E, Zimmer KP, Kelly JW. Gaucher Disease-Associated Glucocerebrosidases Show Mutation-Dependent Chemical Chaperoning Profiles. ACTA ACUST UNITED AC 2005; 12:1235-44. [PMID: 16298303 DOI: 10.1016/j.chembiol.2005.09.007] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Revised: 08/16/2005] [Accepted: 09/20/2005] [Indexed: 11/25/2022]
Abstract
Gaucher disease is a lysosomal storage disorder caused by deficient glucocerebrosidase activity. We have previously shown that the cellular activity of the most common Gaucher disease-associated glucocerebrosidase variant, N370S, is increased when patient-derived cells are cultured with the chemical chaperone N-nonyl-deoxynojirimycin. Chemical chaperones stabilize proteins against misfolding, enabling their trafficking from the endoplasmic reticulum. Herein, the generality of this therapeutic strategy is evaluated with other glucocerebrosidase variants and with additional candidate chemical chaperones. Improved chemical chaperones are identified for N370S glucocerebrosidase. Moreover, we demonstrate that G202R, a glucocerebrosidase variant that is known to be retained in the endoplasmic reticulum, is also amenable to chemical chaperoning. The L444P variant is not chaperoned by any of the active site-directed molecules tested, likely because this mutation destabilizes a domain distinct from the catalytic domain.
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Affiliation(s)
- Anu R Sawkar
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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8
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Královičová J, Christensen MB, Vořechovský I. Biased exon/intron distribution of cryptic and de novo 3' splice sites. Nucleic Acids Res 2005; 33:4882-98. [PMID: 16141195 PMCID: PMC1197134 DOI: 10.1093/nar/gki811] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We compiled sequences of previously published aberrant 3′ splice sites (3′ss) that were generated by mutations in human disease genes. Cryptic 3′ss, defined here as those resulting from a mutation of the 3′YAG consensus, were more frequent in exons than in introns. They clustered in ∼20 nt region adjacent to authentic 3′ss, suggesting that their under-representation in introns is due to a depletion of AG dinucleotides in the polypyrimidine tract (PPT). In contrast, most aberrant 3′ss that were induced by mutations outside the 3′YAG consensus (designated ‘de novo’) were in introns. The activation of intronic de novo 3′ss was largely due to AG-creating mutations in the PPT. In contrast, exonic de novo 3′ss were more often induced by mutations improving the PPT, branchpoint sequence (BPS) or distant auxiliary signals, rather than by direct AG creation. The Shapiro–Senapathy matrix scores had a good prognostic value for cryptic, but not de novo 3′ss. Finally, AG-creating mutations in the PPT that produced aberrant 3′ss upstream of the predicted BPS in vivo shared a similar ‘BPS-new AG’ distance. Reduction of this distance and/or the strength of the new AG PPT in splicing reporter pre-mRNAs improved utilization of authentic 3′ss, suggesting that AG-creating mutations that are located closer to the BPS and are preceded by weaker PPT may result in less severe splicing defects.
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Affiliation(s)
| | | | - Igor Vořechovský
- To whom correspondence should be addressed. Tel: +44 2380 796425; Fax: +44 2380 794264;
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9
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Martin DR, Krum BK, Varadarajan GS, Hathcock TL, Smith BF, Baker HJ. An inversion of 25 base pairs causes feline GM2 gangliosidosis variant. Exp Neurol 2004; 187:30-7. [PMID: 15081585 DOI: 10.1016/j.expneurol.2004.01.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2003] [Revised: 12/19/2003] [Accepted: 01/13/2004] [Indexed: 10/26/2022]
Abstract
In G(M2) gangliosidosis variant 0, a defect in the beta-subunit of lysosomal beta-N-acetylhexosaminidase (EC 3.2.1.52) causes abnormal accumulation of G(M2) ganglioside and severe neurodegeneration. Distinct feline models of G(M2) gangliosidosis variant 0 have been described in both domestic shorthair and Korat cats. In this study, we determined that the causative mutation of G(M2) gangliosidosis in the domestic shorthair cat is a 25-base-pair inversion at the extreme 3' end of the beta-subunit (HEXB) coding sequence, which introduces three amino acid substitutions at the carboxyl terminus of the protein and a translational stop that is eight amino acids premature. Cats homozygous for the 25-base-pair inversion express levels of beta-subunit mRNA approximately 190% of normal and protein levels only 10-20% of normal. Because the 25-base-pair inversion is similar to mutations in the terminal exon of human HEXB, the domestic shorthair cat should serve as an appropriate model to study the molecular pathogenesis of human G(M2) gangliosidosis variant 0 (Sandhoff disease).
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Affiliation(s)
- Douglas R Martin
- Scott-Ritchey Research Center, College of Veterinary Medicine, Auburn University, Auburn, AL 36849-5525, USA.
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10
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Tropak MB, Reid SP, Guiral M, Withers SG, Mahuran D. Pharmacological enhancement of beta-hexosaminidase activity in fibroblasts from adult Tay-Sachs and Sandhoff Patients. J Biol Chem 2004; 279:13478-87. [PMID: 14724290 PMCID: PMC2904802 DOI: 10.1074/jbc.m308523200] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tay-Sachs and Sandhoff diseases are lysosomal storage disorders that result from an inherited deficiency of beta-hexosaminidase A (alphabeta). Whereas the acute forms are associated with a total absence of hexosaminidase A and early death, the chronic adult forms exist with activity and protein levels of approximately 5%, and unaffected individuals have been found with only 10% of normal levels. Surprisingly, almost all disease-associated missense mutations do not affect the active site of the enzyme but, rather, inhibit its ability to obtain and/or retain its native fold in the endoplasmic reticulum, resulting in its retention and accelerated degradation. By growing adult Tay-Sachs fibroblasts in culture medium containing known inhibitors of hexosaminidase we have raised the residual protein and activity levels of intralysosomal hexosaminidase A well above the critical 10% of normal levels. A similar effect was observed in fibroblasts from an adult Sandhoff patient. We propose that these hexosaminidase inhibitors function as pharmacological chaperones, enhancing the stability of the native conformation of the enzyme, increasing the amount of hexosaminidase A capable of exiting the endoplasmic reticulum for transport to the lysosome. Therefore, pharmacological chaperones could provide a novel approach to the treatment of adult Tay-Sachs and possibly Sandhoff diseases.
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Affiliation(s)
- Michael B. Tropak
- Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8
| | - Stephen P. Reid
- Department of Biochemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1
| | - Marianne Guiral
- Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8
| | - Stephen G. Withers
- Department of Biochemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1
| | - Don Mahuran
- Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8
- Department of Laboratory Medicine and Pathology, University of Toronto, Banting Institute, Toronto, Ontario M5G 1L5, Canada
- To whom correspondence should be addressed: Research Institute, Rm. 9146A, Elm Wing, Hospital for Sick Children, 555 University Ave., Toronto M5G 1X8, Ontario. Tel.: 416-813-6161; Fax: 416-813-8700;
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Yoshizawa T, Kohno Y, Nissato S, Shoji S. Compound heterozygosity with two novel mutations in the HEXB gene produces adult Sandhoff disease presenting as a motor neuron disease phenotype. J Neurol Sci 2002; 195:129-38. [PMID: 11897243 DOI: 10.1016/s0022-510x(02)00007-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Little information is available on molecular defects involved in adult Sandhoff disease presenting as motor neuron disease phenotype. We studied enzyme activities of beta-hexosaminidase (Hex) and the HEXB gene encoding the beta-subunit of Hex in a family of the Japanese case. Enzyme assay with 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside revealed a reduction in Hex A and B activity in proband's leukocytes. Although the activity of both in the mother were intermediate between those of controls and the proband, only Hex B reduction determined with heat inactivation was found in the father. Analysis of HEXB gene demonstrated two novel point mutations. The first mutation, IVS2-1G>A, was located at the 3'-splice acceptor site of intron 2 derived from the mother, causing exon 3 skipping. The resultant mRNA encoded a shorter beta-chain, which may not form an active enzyme. The second mutation was a G-to-A transition in exon 13 (c.1598G>A) derived from the father and resulted in arginine-to-histidine substitution at amino acid position 533 (R533H). Expression of R533H mutation in COS-1 cells demonstrated a lack of normal Hex activity, indicating that this mutation is pathological. Compound heterozygosity of these two mutations may trigger the development of adult Sandhoff disease with a motor neuron disease phenotype.
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Affiliation(s)
- Toshihiro Yoshizawa
- Department of Neurology, Institute of Clinical Medicine, University of Tsukuba, 1-1-1 Tennodai, 305-8575, Tsukuba, Japan.
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12
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Triggs-Raine B, Mahuran DJ, Gravel RA. Naturally occurring mutations in GM2 gangliosidosis: a compendium. ADVANCES IN GENETICS 2002; 44:199-224. [PMID: 11596984 DOI: 10.1016/s0065-2660(01)44081-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- B Triggs-Raine
- Department of Biochemistry and Medical Genetics University of Manitoba, Winnipeg, Canada.
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13
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Gomez-Lira M, Mottes M, Perusi C, Pignatti PF, Rizzuto N, Gatti R, Salviati A. A novel 4-bp deletion creates a premature stop codon and dramatically decreases HEXB mRNA levels in a severe case of Sandhoff disease. Mol Cell Probes 2001; 15:75-9. [PMID: 11292324 DOI: 10.1006/mcpr.2000.0342] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We present the molecular genetic analysis of an infantile-onset Sandhoff disease patient. Genomic DNA amplification, heteroduplex analysis, cloning and sequencing revealed a 4-bp deletion in exon 4 (497 DeltaAGTT). The result is a frameshift mutation that leads to a stop codon in exon 5. This mutation is associated with a dramatic decrease of HEXB mRNA levels.
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Affiliation(s)
- M Gomez-Lira
- Dipartimento Materno Infantile e di Biologia e Genetica, Sezione Biologia e Genetica, Università di Verona, Strada Le Grazie 8, Verona, 37134, Italia.
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14
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Kleiman FE, Ramírez AO, Dodelson de Kremer R, Gravel RA, Argaraña CE. A frequent TG deletion near the polyadenylation signal of the human HEXB gene: occurrence of an irregular DNA structure and conserved nucleotide sequence motif in the 3' untranslated region. Hum Mutat 2000; 12:320-9. [PMID: 9792408 DOI: 10.1002/(sici)1098-1004(1998)12:5<320::aid-humu5>3.0.co;2-h] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
While screening for new mutations in the HEXB gene, which encodes the beta-subunit of beta-hexosaminidase, a TG deletion (deltaTG) was found in the 3' untranslated region (3'UTR) of the gene, 7 bp upstream from the polyadenylation signal. Examination of DNA samples of 145 unrelated Argentinean individuals from different racial backgrounds showed that the deltaTG allele was present with a frequency of approximately 0.1, compared with the wild-type (WT) allele. The deletion was not associated with infantile or variant forms of Sandhoff disease when present in combination with a deleterious allele. Total Hex and Hex B enzymatic activities measured in individuals heterozygous for deltaTG and a null allele, IVS-2 + 1G-->A (G-->A), were approximately 30% lower than the activities of G-->A/WT individuals. Analysis of the HEXB mRNA from leukocytes of deltaTG/WT individuals by RT-PCR of the 3'UTR showed that the deltaTG allele is present at lower level than the WT allele. By polyacrylamide gel electrophoresis, it was determined that a PCR fragment containing the +TG version of the 3'UTR of the HEXB gene had an irregular structure. On inspection of genes containing a TG dinucleotide upstream from the polyadenylation signal we found that this dinucleotide was part of a conserved sequence (TGTTTT) immersed in a A/T-rich region. This sequence arrangement was present in more than 40% analyzed eukaryotic mRNAs, including in the human, mouse and cat HEXB genes. The significance of the TG deletion in reference to Sandhoff disease as well as the possible functional role of the consensus sequence and the DNA structure of the 3'UTR are considered.
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Affiliation(s)
- F E Kleiman
- Centro de Investigaciones en Química Biológica de Córdoba-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina
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Abstract
Genotyping individuals for Tay-Sachs disease (TSD) is mainly based on the heat lability of beta-hexosaminidase (Hex) A (alphabeta) and the heat stability of Hex B (betabeta). Mutations in the HEXB gene encoding the beta-subunits of Hex that result in heat-labile Hex B thus may lead to erroneous enzymatic genotyping regarding TSD. Utilizing single strand conformation polymorphism (SSCP) analysis for all 14 exons of HEXB followed by direct sequencing of aberrant fragments, we screened individuals whose Hex B was heat labile. A novel heat labile mutation, previously concluded to exist in the HEXB gene, was identified among Jews and Arabs as 1627 G-->A. One individual with heat labile Hex B (HLB) was negative for this novel mutation and for the known 1514 G-->A HLB mutation, proving that there exists at least one other unidentified HLB mutation. Based on these results, it is advisable to perform DNA tests for 1627 G-->A mutation in suspected HLB individuals.
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Affiliation(s)
- G Narkis
- Department of Human Genetics, Sackler School of Medicine, Tel Aviv University, Israel
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16
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Mahuran DJ. Biochemical consequences of mutations causing the GM2 gangliosidoses. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1455:105-38. [PMID: 10571007 DOI: 10.1016/s0925-4439(99)00074-5] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The hydrolysis of GM2-ganglioside is unusual in its requirements for the correct synthesis, processing, and ultimate combination of three gene products. Whereas two of these proteins are the alpha- (HEXA gene) and beta- (HEXB) subunits of beta-hexosaminidase A, the third is a small glycolipid transport protein, the GM2 activator protein (GM2A), which acts as a substrate specific co-factor for the enzyme. A deficiency of any one of these proteins leads to storage of the ganglioside, primarily in the lysosomes of neuronal cells, and one of the three forms of GM2-gangliosidosis, Tay-Sachs disease, Sandhoff disease or the AB-variant form. Studies of the biochemical impact of naturally occurring mutations associated with the GM2 gangliosidoses on mRNA splicing and stability, and on the intracellular transport and stability of the affected protein have provided some general insights into these complex cellular mechanisms. However, such studies have revealed little in the way of structure-function information on the proteins. It appears that the detrimental effect of most mutations is not specifically on functional elements of the protein, but rather on the proteins' overall folding and/or intracellular transport. The few exceptions to this generalization are missense mutations at two codons in HEXA, causing the unique biochemical phenotype known as the B1-variant, and one codon in both the HEXB and GM2A genes. Biochemical characterization of these mutations has led to the localization of functional residues and/or domains within each of the encoded proteins.
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Affiliation(s)
- D J Mahuran
- Research Institute, The Hospital for Sick Children, Toronto, Ont, Canada.
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17
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Hou Y, McInnes B, Hinek A, Karpati G, Mahuran D. A Pro504 --> Ser substitution in the beta-subunit of beta-hexosaminidase A inhibits alpha-subunit hydrolysis of GM2 ganglioside, resulting in chronic Sandhoff disease. J Biol Chem 1998; 273:21386-92. [PMID: 9694901 DOI: 10.1074/jbc.273.33.21386] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The GM2 gangliosidoses are caused by mutations in the genes encoding the alpha- (Tay-Sachs) or beta- (Sandhoff) subunits of heterodimeric beta-hexosaminidase A (Hex A), or the GM2 activator protein (AB variant), a substrate-specific co-factor for Hex A. Although the active site associated with the hydrolysis of GM2 ganglioside, as well as part of the binding site for the ganglioside-activator complex, is associated with the alpha-subunit, elements of the beta-subunit are also involved. Missense mutations in these genes normally result in the mutant protein being retained in the endoplasmic reticulum and degraded. The mutations associated with the B1-variant of Tay-Sachs are rare exceptions that directly affect residues in the alpha-active site. We have previously reported two sisters with chronic Sandhoff disease who were heterozygous for the common HEXB deletion allele. Cells from these patients had higher than expected levels of mature beta-protein and residual Hex A activity, approximately 20%. We now identify these patients' second mutant allele as a C1510T transition encoding a beta-Pro504 --> Ser substitution. Biochemical characterization of Hex A from both patient cells and cotransfected CHO cells demonstrated that this substitution (a) decreases the level of heterodimer transport out of the endoplasmic reticulum by approximately 45%, (b) lowers its heat stability, (c) does not affect its Km for neutral or charged artificial substrates, and (d) lowers the ratio of units of ganglioside/units of artificial substrate hydrolyzed by a factor of 3. We concluded that the beta-Pro504 --> Ser mutation directly affects the ability of Hex A to hydrolyze its natural substrate but not its artificial substrates. The effect of the mutation on ganglioside hydrolysis, combined with its effect on intracellular transport, produces chronic Sandhoff disease.
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Affiliation(s)
- Y Hou
- The Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
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18
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Mahuran DJ. The GM2 activator protein, its roles as a co-factor in GM2 hydrolysis and as a general glycolipid transport protein. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1393:1-18. [PMID: 9714704 DOI: 10.1016/s0005-2760(98)00057-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although there is only one documented function carried out by the GM2 activator protein in the lysosome, new information suggests that other less obvious roles may also be played by this protein in vivo. This information includes data demonstrating that the GM2 activator is a secretory, as well as a lysosomal protein, and that cells possess a carbohydrate-independent mechanism to re-capture the activator, with or without bound lipid, from the extracellular fluid. Additionally the GM2 activator has been shown to bind, solubilize and transport a broad spectrum of lipid molecules, such as glycolipids, gangliosides and at least one phosphoacylglycerol, between liposomes. At pH 7 the GM2 activator's rate of lipid transport is reduced by only 50% from its maximum rate which is achieved at approx. pH 5, suggesting that the GM2 activator may serve as a general intra- and/or inter-cellular lipid transport protein in vivo. Since the late 1970s the lysosomal form of the GM2 activator has been known to act as a substrate-specific co-factor for the hydrolysis of GM2 ganglioside by beta-hexosaminidase A. Gangliosides are a class of negatively charged glycolipids particularly abundant in neuronal cells which have been linked to numerous in vivo functions, such as memory formation and signal transduction events. Deficiency of the GM2 activator protein results in the storage of GM2 ganglioside and severe neurological disease, the AB-variant form of GM2 gangliosidosis, usually culminating in death before the age of 4 years. The exact mode-of-action of the GM2 activator in its role as a co-factor, and its specificity for various glycolipids are currently matters of debate in the literature.
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Affiliation(s)
- D J Mahuran
- Research Institute, The Hospital for Sick Children, 555 University Ave, Toronto, Ont. M5G 1X8, Canada.
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19
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Gomez-Lira M, Perusi C, Mottes M, Pignatti PF, Rizzuto N, Gatti R, Salviati A. Splicing mutation causes infantile Sandhoff disease. ACTA ACUST UNITED AC 1998. [DOI: 10.1002/(sici)1096-8628(19980123)75:3<330::aid-ajmg21>3.0.co;2-p] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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20
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Abstract
Genetic diseases associated with an enzyme deficiency frequently have reduced intracellular levels of the mutant protein, despite apparently normal levels of message and protein synthesis. It has been suggested that the endoplasmic reticulum (ER) can recognise mutant protein as incorrectly folded and invoke 'quality control' processes which cause the retention and degradation of this protein. This process may occur, even for mutations which do not abrogate protein activity, contributing directly to pathophysiology. Genetic diseases associated with defects in ER and Golgi processing proteins have also been reported and generally result in impaired processing of multiple protein products. In this review the role of the ER and Golgi in the pathogenesis of genetic diseases relating to the vacuolar network are discussed.
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Affiliation(s)
- D A Brooks
- Department of Chemical Pathology, Women's and Children's Hospital, North Adelaide, Australia.
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21
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Pomponio RJ, Reynolds TR, Mandel H, Admoni O, Melone PD, Buck GA, Wolf B. Profound biotinidase deficiency caused by a point mutation that creates a downstream cryptic 3' splice acceptor site within an exon of the human biotinidase gene. Hum Mol Genet 1997; 6:739-45. [PMID: 9158148 DOI: 10.1093/hmg/6.5.739] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Biotinidase recycles the vitamin biotin from biocytin upon the degradation of the biotin-dependent carboxylases. We have identified a novel point mutation within the biotinidase gene that encodes the signal peptide in two unrelated individuals with profound biotinidase deficiency. Sequence analysis of genomic DNA from these individuals revealed a G to A transition (G100-->A) located 57 bases downstream of the authentic splice acceptor site in exon B. Although this mutation predicts a G34S substitution, it also generates a 3' splice acceptor site. Sequence of the PCR-amplified cDNA from the homozygous child revealed that all the product was shorter than that of normal individuals and was the result of aberrant splicing. The aberrantly spliced transcript lacked 57 bases, including a second in-frame ATG, that encode most of the putative signal peptide and results in an in-frame deletion of 19 amino acids. The mutation results in failure to secrete the aberrant protein into the blood. This is the first reported example in which a point mutation creates a cryptic 3' splice acceptor site motif that is used preferentially over the upstream authentic splice site. The preferential usage of the downstream splice site is not consistent with the 5'-3' scanning model, but is consistent with the exon definition model of RNA splicing.
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Affiliation(s)
- R J Pomponio
- Department of Human Genetics, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA
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22
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Adams EM, Becker JA, Griffith L, Segal A, Plotz PH, Raben N. Glycogenosis type II: a juvenile-specific mutation with an unusual splicing pattern and a shared mutation in African Americans. Hum Mutat 1997; 10:128-34. [PMID: 9259196 DOI: 10.1002/(sici)1098-1004(1997)10:2<128::aid-humu5>3.0.co;2-g] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The recessively inherited deficiency of acid alpha-glucosidase (GAA) called Glycogenosis Type II is expressed as three different phenotypes: infantile, juvenile, and adult. At the molecular level, infantile and adult forms of the disease have been extensively studied, but little is known regarding the genetic defects associated with the juvenile form. We describe a novel mutation that defines the intermediate juvenile phenotype in a compound heterozygous patient. A transversion of t to g in intron 6 at position -22 creates a cryptic acceptor site and results in unusual splicing abnormality: insertion of 21 nucleotides of the intronic sequence into mRNA and removal of exon 6 without disruption of the reading frame. The second mutation, Arg854Stop in exon 18, had been previously identified in another African-American patient (Hermans et al., 1993a). Family study indicates that a silent allele harboring the Arg854Stop mutation in our patient is inherited from the patient's father, who is also African-American, thus suggesting a common mutation in this population.
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Affiliation(s)
- E M Adams
- Arthritis and Rheumatism Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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23
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Redonnet-Vernhet I, Mahuran DJ, Salvayre R, Dubas F, Levade T. Significance of two point mutations present in each HEXB allele of patients with adult GM2 gangliosidosis (Sandhoff disease) homozygosity for the Ile207-->Val substitution is not associated with a clinical or biochemical phenotype. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1317:127-33. [PMID: 8950198 DOI: 10.1016/s0925-4439(96)00044-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The molecular defects in the HEXB gene encoding the common beta-subunit of lysosomal beta-hexosaminidase A (beta-Hex A, alpha beta) and beta-Hex B (beta beta) were investigated in a Portuguese family affected with late onset Sandhoff disease (GM2-gangliosidosis variant 0). This family comprised two unaffected daughters and three affected sibs who developed at about age 17 cerebellar ataxia and mental deficiency. Their parents were consanguineous and clinically asymptomatic. There was no detectable beta-Hex B activity and a profound reduction in the activity of beta-Hex A in the leukocytes and transformed lymphoid cell lines from the affected sibs. The expected intermediate values were observed in the parents as well as in one daughter and her children. Western analysis revealed the presence of reduced, but detectable amounts of mature beta-chain protein in cell lysates from the probands and intermediate levels in the parents. Nucleotide sequencing of amplified, reverse-transcribed beta-chain mRNA demonstrated the presence of two single point mutations: an A619 to G transition in exon 5 (Ile207-->Val), and a G1514 to A transition in exon 13 (Arg505-->Gln). Both of these two mutations have been previously linked to the adult form of Sandhoff disease in compound heterozygote patients. All three affected sibs were found to be homoallelic for both mutations. Interestingly, while the mother was heterozygous for each mutation, the father was homozygote for the A619-->G substitution and heterozygote for the G1514-->A transition. Since the father is homozygote for the A619-->G mutation but expresses a biochemical phenotype consistent with a carrier of Sandhoff disease and is clinically asymptomatic, this substitution is likely a neutral mutation. We confirmed this hypothesis by finding this transition present in 4 of 30 alleles from normal individuals. We conclude that homozygosity for the G1514-->A mutation is exclusively responsible for the adult form of Sandhoff disease in this family, and that the A619-->G substitution is not a deleterious mutation but rather a common HEXB polymorphism.
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Affiliation(s)
- I Redonnet-Vernhet
- Laboratoire de Biochimie Médicale, CJF INSERM 9206, Institut Louis Bugnard, Toulouse, France
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24
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Affiliation(s)
- V Gieselmann
- Department of Biochemistry II, Georg August Universität, Göttingen, Germany
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25
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Gomez-Lira M, Perusi C, Brutti N, Farnetani MA, Margollicci MA, Rizzuto N, Pignatti PF, Salviati A. A 48-bp insertion between exon 13 and 14 of the HEXB gene causes infantile-onset Sandhoff disease. Hum Mutat 1995; 6:260-2. [PMID: 8535449 DOI: 10.1002/humu.1380060313] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- M Gomez-Lira
- Istituto di Biologia e Genetica, Università di Verona, Italy
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26
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Bolhuis PA, Ponne NJ, Bikker H, Baas F, Vianney de Jong JM. Molecular basis of an adult form of Sandhoff disease: substitution of glutamine for arginine at position 505 of the beta-chain of beta-hexosaminidase results in a labile enzyme. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1182:142-6. [PMID: 8357844 DOI: 10.1016/0925-4439(93)90134-m] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Sandhoff disease is a lysosomal storage disorder characterized by accumulation of GM2 ganglioside due to mutations in the beta-chain of beta-hexosaminidase. Hexosaminidase activity is negligible in infantile Sandhoff disease whereas residual activity is present in juvenile and adult forms. Here we report the molecular basis of the first described adult form of Sandhoff disease. Southern analysis of chromosomal DNA indicated the absence of chromosomal deletions in the gene encoding the beta-chain. Northern analysis of RNA from cultured fibroblasts demonstrated that at least one of the beta-chain alleles was transcribed into normal-length mRNA. Sequence analysis of the entire cDNA prepared from poly-adenylated RNA showed that only one point mutation was present, consisting of a G-->A transition at nucleotide position 1514. This mutation changes the electric charge at amino acid position 505 by substitution of glutamine for arginine in a highly conserved part of the beta-chain, present even in the slime mold Dictyostelium discoideum. The nucleotide transition generated a new restriction site for DdeI, which was present in only one of the alleles of the patient. Reverse transcription of mRNA followed by restriction with DdeI resulted in complete digestion at the mutation site, demonstrating that the second allele was of an mRNA-negative type. Transfection of COS cells with a cDNA construct containing the mutation but otherwise the normal sequence resulted in the expression of a labile form of beta-hexosaminidase. These results show that the patient's is a genetic compound, and that the lability of beta-hexosaminidase found in this form of Sandhoff disease is based on a single nucleotide transition.
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Affiliation(s)
- P A Bolhuis
- Academic Medical Center, Department of Neurology, Amsterdam, The Netherlands
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27
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Moskowitz SM, Tieu PT, Neufeld EF. Mutation in Scheie syndrome (MPS IS): a G-->A transition creates new splice site in intron 5 of one IDUA allele. Hum Mutat 1993; 2:141-4. [PMID: 8318992 DOI: 10.1002/humu.1380020215] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- S M Moskowitz
- Department of Biological Chemistry, School of Medicine, University of California, Los Angeles 90024-1737
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28
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Brown CA, McInnes B, de Kremer RD, Mahuran DJ. Characterization of two HEXB gene mutations in Argentinean patients with Sandhoff disease. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1180:91-8. [PMID: 1390948 DOI: 10.1016/0925-4439(92)90031-h] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Beta-hexosaminidase A (beta-N-acetyl-D-hexosaminidase, EC 3.2.1.5.2) is a lysosomal hydrolase composed of an alpha- and a beta-subunit. It is responsible for the degradation of GM2 ganglioside. Mutations in the HEXB gene encoded beta-subunit cause a form of GM2 gangliosidosis known as Sandhoff disease. Although this is a rare disease in the general population, several geographically isolated groups have a high carrier frequency. Most notably, a 1 in 16-29 carrier frequency has been reported for an Argentinean population living in an area contained within a 375-km radius from Córdoba. Analysis of the genomic DNA of two patients from this region revealed that one was homozygous for a G to A substitution at the 5' donor splice site of intron 2. This mutation completely abolishes normal mRNA splicing. The other patient was a compared of the intron 2 G-->A substitution and a second allele due to a 4-bp deletion in exon 7. The beta-subunit mRNA of this allele is unstable, presumably as a result of an early stop codon introduced by the deletion. Two novel PCR-based assays were developed to detect these mutations. We suggest that one of these assays could be modified and used as a rapid screening procedure for 5' donor splice site defects in other genes. These results provide a further example of the genetic heterogeneity that can exist even in a small geographically isolated population.
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Affiliation(s)
- C A Brown
- Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada
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29
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McInnes B, Brown CA, Mahuran DJ. Two small deletion mutations of the HEXB gene are present in DNA from a patient with infantile Sandhoff disease. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1138:315-7. [PMID: 1532910 DOI: 10.1016/0925-4439(92)90009-c] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Lysosomal beta-hexosaminidase (EC 3.2.1.52) occurs as two major isozymes hexosaminidase A (alpha beta) and B (beta beta). The alpha subunit is encoded by the HEXA gene and the beta subunit by HEXB gene. Defects in the alpha or beta subunits lead to Tay-Sachs or Sandhoff disease, respectively. While many HEXA gene mutations have been reported only three HEXB gene mutations are known. We report the characterization of two rare HEXB mutations present in genomic DNA from a single fibroblast cell line, GM203, taken from a patient with the infantile form of Sandhoff disease. The first is a single base pair deletion in exon 7 changing the codon for Gly-258, GGA, to GA and the second, a two base pair deletion in exon 11 changes the codons for Arg-435/Val-436, AGA/GTC, to AGTC. Each mutation produces a frame shift in the affected allele that results in a premature stop codon 17 or 20 codons downstream, respectively. These mutations also result in the inability to detect beta-mRNA by Northern blot analysis of total mRNA. These data are consistent with the idea that the severe infantile form of Tay-Sachs or Sandhoff disease is associated with a total lack of residual hexosaminidase A activity.
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Affiliation(s)
- B McInnes
- Research Institute, Hospital for Sick Children, Toronto, Canada
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30
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Hasilik A. The early and late processing of lysosomal enzymes: proteolysis and compartmentation. EXPERIENTIA 1992; 48:130-51. [PMID: 1740186 DOI: 10.1007/bf01923507] [Citation(s) in RCA: 123] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Lysosomal enzymes are subjected to a number of modifications including carbohydrate restructuring and proteolytic maturation. Some of these reactions support lysosomal targeting, others are necessary for activation or keeping the enzyme inactive before being segregated, while still others may be adventitious. The non-segregated fraction of the enzyme is secreted and can be isolated from the medium. It is considered that the secreted lysosomal enzymes fulfill certain physiological and pathophysiological roles. By comparing the secreted and the intracellular enzymes it is possible to distinguish between the reactions that occur before and after the segregation. In this review the reactions that may influence the segregation are referred to as the early processing and those characteristic for the enzymes isolated from lysosomal compartments as the late processing. The early processing is characterized mainly by modifications of carbohydrate side chains. In the late processing, proteolytic fragmentation represents the most conspicuous changes. The review focuses on the compartmentation of the reactions and the proteolytic fragmentation of lysosomal enzyme precursors. While a plethora of proteolytic reactions are involved, our knowledge of the proteinases responsible for the particular maturation reactions remains very limited. The review points also to work with cells from patients affected with lysosomal storage disorders, which contributed to our understanding of the lysosomal apparatus.
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Affiliation(s)
- A Hasilik
- Institute for Physiological Chemistry and Pathobiochemistry, University of Münster, Germany
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31
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Wakamatsu N, Kobayashi H, Miyatake T, Tsuji S. A novel exon mutation in the human beta-hexosaminidase beta subunit gene affects 3' splice site selection. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)45894-2] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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32
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Banerjee P, Siciliano L, Oliveri D, McCabe NR, Boyers MJ, Horwitz AL, Li SC, Dawson G. Molecular basis of an adult form of beta-hexosaminidase B deficiency with motor neuron disease. Biochem Biophys Res Commun 1991; 181:108-15. [PMID: 1720305 DOI: 10.1016/s0006-291x(05)81388-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A patient (KL) with progressive motor neuron disease associated with partial Hex A (alpha beta) and no Hex B (beta beta) activity, synthesized beta-chains which only associated with alpha-chains. To identify the molecular basis of this inability of beta-chains to self associate, RNA from cultured fibroblasts was reverse transcribed, the cDNA encoding the beta-chain amplified by polymerase chain reaction, subcloned, and sequenced to reveal two types of single missense mutation. The first mutation, (Type I) 619A----G, was paternally inherited and converted a 207IIe----Val in a highly conserved region believed to be associated with catalytic activity and activator protein binding. Biochemical evidence for impaired activator protein binding was obtained by purifying Hex A from KL urine and demonstrating a greater than 50% reduction of in vitro GM2 hydrolysis compared to normal urinary Hex A. In other cDNA species (Type II), a maternally inherited 1367A----C mutation converted 456Tyr----Ser in another highly conserved region of the beta-chain and we propose that this mutation leads to the inability of the beta-chains to self associate and thus reach maturity. These same cDNA species contained a second 362A----G mutation which converted 121Lys----Arg, but is apparently a polymorphism since it also occurs in some normal subjects. We propose that the patient is a compound heterozygote in which a combination of no self-association of the mutant beta-chains and impaired activator protein binding to alpha-beta (mutant) (Hex A) required for GM2 hydrolysis result in total beta-Hex B deficiency and slow accumulation of GM2 ganglioside, primarily in motor neurons.
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Affiliation(s)
- P Banerjee
- Joseph P. Kennedy, Jr. Mental Retardation Research Center, Department of Pediatrics, University of Chicago, IL 60637
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