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Molecular Characterization of Portuguese Patients with Hereditary Cerebellar Ataxia. Cells 2022; 11:cells11060981. [PMID: 35326432 PMCID: PMC8946949 DOI: 10.3390/cells11060981] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/10/2022] [Accepted: 03/11/2022] [Indexed: 01/02/2023] Open
Abstract
Hereditary cerebellar ataxia (HCA) comprises a clinical and genetic heterogeneous group of neurodegenerative disorders characterized by incoordination of movement, speech, and unsteady gait. In this study, we performed whole-exome sequencing (WES) in 19 families with HCA and presumed autosomal recessive (AR) inheritance, to identify the causal genes. A phenotypic classification was performed, considering the main clinical syndromes: spastic ataxia, ataxia and neuropathy, ataxia and oculomotor apraxia (AOA), ataxia and dystonia, and ataxia with cognitive impairment. The most frequent causal genes were associated with spastic ataxia (SACS and KIF1C) and with ataxia and neuropathy or AOA (PNKP). We also identified three families with autosomal dominant (AD) forms arising from de novo variants in KIF1A, CACNA1A, or ATP1A3, reinforcing the importance of differential diagnosis (AR vs. AD forms) in families with only one affected member. Moreover, 10 novel causal-variants were identified, and the detrimental effect of two splice-site variants confirmed through functional assays. Finally, by reviewing the molecular mechanisms, we speculated that regulation of cytoskeleton function might be impaired in spastic ataxia, whereas DNA repair is clearly associated with AOA. In conclusion, our study provided a genetic diagnosis for HCA families and proposed common molecular pathways underlying cerebellar neurodegeneration.
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Rashid S, Shah S, Bar-Joseph Z, Pandya R. Dhaka: variational autoencoder for unmasking tumor heterogeneity from single cell genomic data. Bioinformatics 2021; 37:1535-1543. [PMID: 30768159 PMCID: PMC11025345 DOI: 10.1093/bioinformatics/btz095] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 01/18/2019] [Accepted: 02/13/2019] [Indexed: 12/22/2022] Open
Abstract
MOTIVATION Intra-tumor heterogeneity is one of the key confounding factors in deciphering tumor evolution. Malignant cells exhibit variations in their gene expression, copy numbers and mutation even when originating from a single progenitor cell. Single cell sequencing of tumor cells has recently emerged as a viable option for unmasking the underlying tumor heterogeneity. However, extracting features from single cell genomic data in order to infer their evolutionary trajectory remains computationally challenging due to the extremely noisy and sparse nature of the data. RESULTS Here we describe 'Dhaka', a variational autoencoder method which transforms single cell genomic data to a reduced dimension feature space that is more efficient in differentiating between (hidden) tumor subpopulations. Our method is general and can be applied to several different types of genomic data including copy number variation from scDNA-Seq and gene expression from scRNA-Seq experiments. We tested the method on synthetic and six single cell cancer datasets where the number of cells ranges from 250 to 6000 for each sample. Analysis of the resulting feature space revealed subpopulations of cells and their marker genes. The features are also able to infer the lineage and/or differentiation trajectory between cells greatly improving upon prior methods suggested for feature extraction and dimensionality reduction of such data. AVAILABILITY AND IMPLEMENTATION All the datasets used in the paper are publicly available and developed software package and supporting info is available on Github https://github.com/MicrosoftGenomics/Dhaka. SUPPLEMENTARY INFORMATION Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Sabrina Rashid
- Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA 15232, USA
| | - Sohrab Shah
- Department of Computer Science
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
- Department of Molecular Oncology, BC Cancer Agency, Vancouver, BC V5Z 4E6, Canada
| | - Ziv Bar-Joseph
- Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA 15232, USA
- Machine Learning Department, Carnegie Mellon University, Pittsburgh, PA 15232, USA
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Identification of mutations in HEXA and HEXB in Sandhoff and Tay-Sachs diseases: a new large deletion caused by Alu elements in HEXA. Hum Genome Var 2018; 5:18003. [PMID: 31428437 PMCID: PMC6694291 DOI: 10.1038/hgv.2018.3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 12/21/2017] [Accepted: 12/21/2017] [Indexed: 12/12/2022] Open
Abstract
GM2 gangliosides are a group of lysosomal lipid storage disorders that are due to mutations in HEXA, HEXB and GM2A. In our study, 10 patients with these diseases were enrolled, and Sanger sequencing was performed for the HEXA and HEXB genes. The results revealed one known splice site mutation (c.346+1G>A, IVS2+1G>A) and three novel mutations (a large deletion involving exons 6–10; one nucleotide deletion, c.622delG [p.D208Ifsx15]; and a missense mutation, c.919G>A [p.E307K]) in HEXA. In HEXB, one known mutation (c.1597C>T [p.R533C]) and one variant of uncertain significance (c.619A>G [p.I207V]) were identified. Five patients had c.1597C>T in HEXB, indicating a common mutation in south Iran. In this study, a unique large deletion in HEXA was identified as a homozygous state. To predict the cause of the large deletion in HEXA, RepeatMasker was used to investigate the Alu elements. In addition, to identify the breakpoint of this deletion, PCR was performed around these elements. Using Repeat masker, different Alu elements were identified across HEXA, mainly in intron 5 and intron 10 adjacent to the deleted exons. PCR around the Alu elements and Sanger sequencing revealed the start point of a large deletion in AluSz6 in the intron 6 and the end of its breakpoint 73 nucleotides downstream of AluJo in intron 10. Our study showed that HEXA is an Alu-rich gene that predisposes individuals to disease-associated large deletions due to these elements.
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Zhang W, Zeng H, Huang Y, Xie T, Zheng J, Zhao X, Sheng H, Liu H, Liu L. Clinical,biochemical and molecular analysis of five Chinese patients with Sandhoff disease. Metab Brain Dis 2016; 31:861-7. [PMID: 27021291 DOI: 10.1007/s11011-016-9819-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 03/02/2016] [Indexed: 11/25/2022]
Abstract
Sandhoff disease (SD) is a rare autosomal recessive lysosomal storage disorder of sphingolipid metabolism resulting from the deficiency of β-hexosaminidase (HEX). Mutations of the HEXB gene cause Sandhoff disease. In order to improve the diagnosis and expand the knowledge of the disease, we collected and analyzed relevant data of clinical diagnosis, biochemical investigation, and molecular mutational analysis in five Chinese patients with SD. The patients presented with heterogenous symptoms of neurologic deterioration. HEX activity in leukocytes was severely deficient. We identified seven different mutations, including three known mutations: IVS12-26G > A, p.T209I, p.I207V, and four novel mutations: p.P468PfsX62, p.L223P, p.Y463X, p.G549R. We also detected two different heterozygous mutations c.-122delC and c.-126C > T in the promoter which were suspected to be deleterious mutations. We attempted to correlate these mutations with the clinical presentation of the patients. Our study indicates that the mutation p.T209I and p.P468PfsX62 may link to the infantile form of SD. Our study expands the spectrum of genotype of SD in China, provides new insights into the molecular mechanism of SD and helps to the diagnosis and treatment of this disease.
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Affiliation(s)
- Wen Zhang
- Department of Pediatrics, The First Affiliated Hospital, Jinan University, Guangzhou, Guangdong, China
| | - Huasong Zeng
- Department of Immunology and Rheumatology, Guangzhou Women and Children's Medical Center, Guangzhou, Guangdong, China
| | - Yonglan Huang
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China.
| | - Ting Xie
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China
| | - Jipeng Zheng
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China
| | - Xiaoyuan Zhao
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China
| | - Huiying Sheng
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China
| | - Hongsheng Liu
- Department of Radiology, Guangzhou Women and Children's Medical Center, Guangzhou, Guangdong, China
| | - Li Liu
- Department of Genetics and Endocrinology, Guangzhou Women and Children's Medical Center, 9 Jinsui Road, Guangzhou, Guangdong, 510623, China.
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Fitterer B, Hall P, Antonishyn N, Desikan R, Gelb M, Lehotay D. Incidence and carrier frequency of Sandhoff disease in Saskatchewan determined using a novel substrate with detection by tandem mass spectrometry and molecular genetic analysis. Mol Genet Metab 2014; 111:382-389. [PMID: 24461908 PMCID: PMC4346577 DOI: 10.1016/j.ymgme.2014.01.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 01/04/2014] [Accepted: 01/05/2014] [Indexed: 11/21/2022]
Abstract
Sandhoff disease is a rare progressive neurodegenerative genetic disorder with a high incidence among certain isolated communities and ethnic groups around the world. Previous reports have shown a high occurrence of Sandhoff disease in northern Saskatchewan. Newborn screening cards from northern Saskatchewan were retrospectively screened in order to investigate the incidence and determine the carrier frequency of Sandhoff disease in these communities. PCR-based screening was conducted for the c.115delG (p.(Val39fs)) variant in the HEXB gene that was previously found in 4 Sandhoff disease patients from this area. The carrier frequency for this allele was estimated to be ~1:27. MS/MS-based screening of hexosaminidase activity along with genetic sequencing allowed for the identification of additional variants based on low total hexosaminidase activity and high % hexosaminidase A activity relative to c.115delG carriers. In total 4 pathogenic variants were discovered in the population (c.115delG, c.619A>G, c.1601G>T, and c.1652G>A) of which two are previously unreported (c.1601G>T and c.1652G>A). The combined carrier frequency of these alleles in the study area was estimated at ~1:15. Based on the number of cases of Sandhoff disease from this area we estimate the incidence to be ~1:390 corresponding to a child being born with the disease every 1-2 years on average. The results from our study were then compared with variants in the HEXB gene from the genomes available from the 1000 Genomes project. A total of 19 HEXB variants were found in the 1092 genomes of which 5 are suspected of having a deleterious effect on hexosaminidase activity. The estimated carrier frequency of Sandhoff disease in Saskatchewan at 1:15 is more than 3 times higher than the carrier frequency in the global sample provided by the 1000 Genomes project at 1:57.
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Affiliation(s)
- Braden Fitterer
- Molecular Diagnostics, Saskatchewan Disease Control Laboratory, 5 Research Drive, Regina, SK S4S 0A4, Canada.
| | - Patricia Hall
- Molecular Diagnostics, Saskatchewan Disease Control Laboratory, 5 Research Drive, Regina, SK S4S 0A4, Canada; Department of Human Genetics, Emory University, Atlanta, GA 30033, USA.
| | - Nick Antonishyn
- Molecular Diagnostics, Saskatchewan Disease Control Laboratory, 5 Research Drive, Regina, SK S4S 0A4, Canada.
| | - Rajagopal Desikan
- Department of Chemistry, Campus Box 351700, University of Washington, Seattle, WA 98195, USA; Department of Biochemistry, Campus Box 351700, University of Washington, Seattle, WA 98195, USA
| | - Michael Gelb
- Department of Chemistry, Campus Box 351700, University of Washington, Seattle, WA 98195, USA; Department of Biochemistry, Campus Box 351700, University of Washington, Seattle, WA 98195, USA.
| | - Denis Lehotay
- Molecular Diagnostics, Saskatchewan Disease Control Laboratory, 5 Research Drive, Regina, SK S4S 0A4, Canada.
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Yasui N, Takaoka Y, Nishio H, Nurputra DK, Sekiguchi K, Hamaguchi H, Kowa H, Maeda E, Sugano A, Miura K, Sakaeda T, Kanda F, Toda T. Molecular pathology of Sandhoff disease with p.Arg505Gln in HEXB: application of simulation analysis. J Hum Genet 2013; 58:611-7. [DOI: 10.1038/jhg.2013.68] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Revised: 05/15/2013] [Accepted: 05/19/2013] [Indexed: 11/09/2022]
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Yamada K, Takado Y, Kato YS, Yamada Y, Ishiguro H, Wakamatsu N. Characterization of the mutant β-subunit of β-hexosaminidase for dimer formation responsible for the adult form of Sandhoff disease with the motor neuron disease phenotype. J Biochem 2012; 153:111-9. [PMID: 23127958 DOI: 10.1093/jb/mvs131] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The adult form of Sandhoff disease with the motor neuron disease phenotype is a rare neurodegenerative disorder caused by mutations in HEXB encoding the β-subunit of β-hexosaminidase, yet the properties of mutant β-subunits of the disease have not been fully determined. We identified a novel mutation (H235Y) in the β-sheet of the (β/α)₈-barrel domain, in addition to the previously reported P417L mutation that causes aberrant splicing, in a Japanese patient with the motor neuron disease phenotype. Enzyme assays, gel filtration studies and immunoprecipitation studies with HEK293 cells transiently expressing mutant β-subunits demonstrated that the H235Y mutation abolished both α-β and β-β dimer formation without increasing β-hexosaminidase activity, whereas other reported mutant β-subunits (Y456S, P504S or R533H) associated with the motor neuron disease phenotype formed dimers. Structural analysis suggested that the H235Y mutation in the β-sheet of the (β/α)₈-barrel domain changed the conformation of the β-subunit by causing a clash with the E288 side chain. In summary, H235Y is the first mutation in the β-sheet of the (β/α)₈-barrel domain of the β-subunit that abolishes α-β and β-β dimer formation; the presented patient is the second patient to exhibit the motor neuron disease phenotype with P417L and a non-functional allele of HEXB.
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Affiliation(s)
- Kenichiro Yamada
- Department of Genetics, Institute for Developmental Research, Aichi Human Service Center, 713-8 Kamiya-cho, Kasugai, Aichi 480-0392, Japan
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Molecular and functional analysis of the HEXB gene in Italian patients affected with Sandhoff disease: identification of six novel alleles. Neurogenetics 2008; 10:49-58. [PMID: 18758829 DOI: 10.1007/s10048-008-0145-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2008] [Accepted: 08/07/2008] [Indexed: 10/21/2022]
Abstract
We report the molecular characterization of 12 unrelated Italian patients affected with Sandhoff disease (SD), a recessively inherited disorder caused by mutations in HEXB gene. We identified 11 different mutations of which six are novel: one large deletion of 2,406 nt, (c.299+1471_408del2406), one frameshift mutation c.965delT (p.I322fsX32), one nonsense c.1372C>T (p.Q458X), and three splicing mutations (c.299G>T, c.300-2A>G and c.512-1G>T). One allele was only characterized at the messenger RNA (mRNA) level (r = 1170_1242del). Real-time polymerase chain reaction analysis of the HEXB mRNA from fibroblasts derived from patients carrying the novel point mutations showed that the presence of the premature termination codon in the transcript bearing the mutation c.965delT triggers the nonsense-mediated decay (NMD) pathway, which results in the degradation of the aberrant mRNA. The presence of the c.299G>T mutation leads to the degradation of the mutated mRNA by a mechanism other than NMD, while mutations c.300-2A>G and c.512-1G>T cause the expression of aberrant transcripts. In our group, the most frequent mutation was c.850C>T (p.R284X) representing 29% of the alleles. Haplotype analysis suggested that this mutation did not originate from a single genetic event. Interestingly, the common 16-kb deletion mutation was absent. This work provides valuable information regarding the molecular genetics of SD in Italy and provides new insights into the molecular basis of the disease.
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Mark BL, Mahuran DJ, Cherney MM, Zhao D, Knapp S, James MNG. Crystal structure of human beta-hexosaminidase B: understanding the molecular basis of Sandhoff and Tay-Sachs disease. J Mol Biol 2003; 327:1093-109. [PMID: 12662933 PMCID: PMC2910754 DOI: 10.1016/s0022-2836(03)00216-x] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In humans, two major beta-hexosaminidase isoenzymes exist: Hex A and Hex B. Hex A is a heterodimer of subunits alpha and beta (60% identity), whereas Hex B is a homodimer of beta-subunits. Interest in human beta-hexosaminidase stems from its association with Tay-Sachs and Sandhoff disease; these are prototypical lysosomal storage disorders resulting from the abnormal accumulation of G(M2)-ganglioside (G(M2)). Hex A degrades G(M2) by removing a terminal N-acetyl-D-galactosamine (beta-GalNAc) residue, and this activity requires the G(M2)-activator, a protein which solubilizes the ganglioside for presentation to Hex A. We present here the crystal structure of human Hex B, alone (2.4A) and in complex with the mechanistic inhibitors GalNAc-isofagomine (2.2A) or NAG-thiazoline (2.5A). From these, and the known X-ray structure of the G(M2)-activator, we have modeled Hex A in complex with the activator and ganglioside. Together, our crystallographic and modeling data demonstrate how alpha and beta-subunits dimerize to form either Hex A or Hex B, how these isoenzymes hydrolyze diverse substrates, and how many documented point mutations cause Sandhoff disease (beta-subunit mutations) and Tay-Sachs disease (alpha-subunit mutations).
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Affiliation(s)
- Brian L. Mark
- Canadian Institutes of Heath Research Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alt.,Canada T6G 2H7
| | - Don J. Mahuran
- The Research Institute, The Hospital for Sick Children, 555 University Ave, Toronto Ont., Canada M5G1X8
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ont., Canada M5G1L6
| | - Maia M. Cherney
- Canadian Institutes of Heath Research Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alt.,Canada T6G 2H7
| | - Dalian Zhao
- Department of Chemistry, Rutgers University, New Brunswick, NJ 08903, USA
| | - Spencer Knapp
- Department of Chemistry, Rutgers University, New Brunswick, NJ 08903, USA
| | - Michael N. G. James
- Canadian Institutes of Heath Research Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alt.,Canada T6G 2H7
- Corresponding author:
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Utsumi K, Tsuji A, Kase R, Tanaka A, Tanaka T, Uyama E, Ozawa T, Sakuraba H, Komaba Y, Kawabe M, Iino Y, Katayama Y. Western blotting analysis of the beta-hexosaminidase alpha- and beta-subunits in cultured fibroblasts from cases of various forms of GM2 gangliosidosis. Acta Neurol Scand 2002; 105:427-30. [PMID: 12027830 DOI: 10.1034/j.1600-0404.2002.01097.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
OBJECTIVES 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. MATERIALS AND METHODS 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. RESULTS 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. CONCLUSION This method is easy and sensitive for detecting target proteins, and is useful for clarification of the pathophysiologies of GM2 gangliosidoses.
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Affiliation(s)
- K Utsumi
- The Second Department of Internal Medicine, Nippon Medical School, Bunkyo-ku, Tokyo, Japan. utsumi_kouichi/
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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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12
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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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13
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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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14
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Chavany C, Jendoubi M. Biology and potential strategies for the treatment of GM2 gangliosidoses. MOLECULAR MEDICINE TODAY 1998; 4:158-65. [PMID: 9572057 DOI: 10.1016/s1357-4310(98)01227-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The GM2 gangliosidoses are a group of heritable neurodegenerative disorders caused by excessive accumulation of the ganglioside GM2 owing to deficiency in beta-hexosaminidase activity. Tay-Sachs and Sandhoff diseases have similar clinical phenotypes resulting from a deficiency in human hexosaminidase alpha and beta subunits, respectively. The lack of treatment for GM2 gangliosidoses stimulated interest in developing animal models to understand the molecular mechanisms underlying the various forms of this disease and to test new potential therapies. In this review, we discuss the molecular biology of GM2 gangliosidoses and the different strategies that have been tested in animal models for the treatment of this genetic disorder, including gene transfer and cell engraftment of neural stem cells engineered to express the hexosaminidase isoenzymes.
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Affiliation(s)
- C Chavany
- Genetics and Molecular Immunology Section, National Institutes of Health, Bethesda, MD 20892, USA
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Hara A, Uyama E, Uchino M, Shimmoto M, Utsumi K, Itoh K, Kase R, Naito M, Sugiyama E, Taketomi T, Sukegawa K, Sakuraba H. Adult Sandhoff's disease: R505Q and I207V substitutions in the HEXB gene of the first Japanese case. J Neurol Sci 1998; 155:86-91. [PMID: 9562328 DOI: 10.1016/s0022-510x(97)00299-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We describe a 31-year-old Japanese man with adult Sandhoff s disease presenting as spinocerebellar degeneration. There was a marked cerebellar atrophy on MRI, and proliferation of abundant PAS-positive foamy macrophages in the rectal mucosa. The activities of total beta-Hex, beta-Hex A, and beta-Hex B in leucocytes of the patient were 14%, 15%, and 6% of control values, respectively. However, oligosacchariduria or ultrastructural storage materials in liver tissue were nil. Direct sequencing of cDNA and genomic DNA, and restriction digestion revealed two different homozygous base substitutions in the HEXB gene: the G1514-->A substitution (R505Q) and the A619-->G substitution (1207V). The parents were consanguineous. His healthy mother, an enzymatic heterozygous carrier, was homozygous for 1207V, but heterozygous for R505Q mutation. Thus, the patient is probably homozygous for both base substitutions and a R505Q mutation may be linked to the phenotype of adult Sandhoff's disease.
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Affiliation(s)
- A Hara
- Department of Neurology, Kumamoto University School of Medicine, Japan
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Redonnet-Vernhet I, Chatelut M, Buscail L, Mahuran DJ, Salvayre R, Levade T. A619→G substitution in the HEXB gene is not a deleterious mutation, but a frequent polymorphism. Hum Mutat 1998. [DOI: 10.1002/humu.13801101110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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