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Monckton DG. The Contribution of Somatic Expansion of the CAG Repeat to Symptomatic Development in Huntington's Disease: A Historical Perspective. J Huntingtons Dis 2021; 10:7-33. [PMID: 33579863 PMCID: PMC7990401 DOI: 10.3233/jhd-200429] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The discovery in the early 1990s of the expansion of unstable simple sequence repeats as the causative mutation for a number of inherited human disorders, including Huntington’s disease (HD), opened up a new era of human genetics and provided explanations for some old problems. In particular, an inverse association between the number of repeats inherited and age at onset, and unprecedented levels of germline instability, biased toward further expansion, provided an explanation for the wide symptomatic variability and anticipation observed in HD and many of these disorders. The repeats were also revealed to be somatically unstable in a process that is expansion-biased, age-dependent and tissue-specific, features that are now increasingly recognised as contributory to the age-dependence, progressive nature and tissue specificity of the symptoms of HD, and at least some related disorders. With much of the data deriving from affected individuals, and model systems, somatic expansions have been revealed to arise in a cell division-independent manner in critical target tissues via a mechanism involving key components of the DNA mismatch repair pathway. These insights have opened new approaches to thinking about how the disease could be treated by suppressing somatic expansion and revealed novel protein targets for intervention. Exciting times lie ahead in turning these insights into novel therapies for HD and related disorders.
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Affiliation(s)
- Darren G Monckton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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2
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Thomas JD, Sznajder ŁJ, Bardhi O, Aslam FN, Anastasiadis ZP, Scotti MM, Nishino I, Nakamori M, Wang ET, Swanson MS. Disrupted prenatal RNA processing and myogenesis in congenital myotonic dystrophy. Genes Dev 2017; 31:1122-1133. [PMID: 28698297 PMCID: PMC5538435 DOI: 10.1101/gad.300590.117] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Accepted: 05/26/2017] [Indexed: 02/06/2023]
Abstract
Thomas et al. demonstrate that RNA misprocessing is a major pathogenic factor in congenital myotonic dystrophy and provide novel mouse models to further examine roles for cotranscriptional/post-transcriptional gene regulation during tissue development. Myotonic dystrophy type 1 (DM1) is a CTG microsatellite expansion (CTGexp) disorder caused by expression of CUGexp RNAs. These mutant RNAs alter the activities of RNA processing factors, including MBNL proteins, leading to re-expression of fetal isoforms in adult tissues and DM1 pathology. While this pathogenesis model accounts for adult-onset disease, the molecular basis of congenital DM (CDM) is unknown. Here, we test the hypothesis that disruption of developmentally regulated RNA alternative processing pathways contributes to CDM disease. We identify prominent alternative splicing and polyadenylation abnormalities in infant CDM muscle, and, although most are also misregulated in adult-onset DM1, dysregulation is significantly more severe in CDM. Furthermore, analysis of alternative splicing during human myogenesis reveals that CDM-relevant exons undergo prenatal RNA isoform transitions and are predicted to be disrupted by CUGexp-associated mechanisms in utero. To test this possibility and the contribution of MBNLs to CDM pathogenesis, we generated mouse Mbnl double (Mbnl1; Mbnl2) and triple (Mbnl1; Mbnl2; Mbnl3) muscle-specific knockout models that recapitulate the congenital myopathy, gene expression, and spliceopathy defects characteristic of CDM. This study demonstrates that RNA misprocessing is a major pathogenic factor in CDM and provides novel mouse models to further examine roles for cotranscriptional/post-transcriptional gene regulation during development.
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Affiliation(s)
- James D Thomas
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Łukasz J Sznajder
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Olgert Bardhi
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Faaiq N Aslam
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Zacharias P Anastasiadis
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Marina M Scotti
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Ichizo Nishino
- Department of Neuromuscular Research, National Center of Neurology and Psychiatry, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
| | - Masayuki Nakamori
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
| | - Eric T Wang
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Maurice S Swanson
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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Barbé L, Lanni S, López-Castel A, Franck S, Spits C, Keymolen K, Seneca S, Tomé S, Miron I, Letourneau J, Liang M, Choufani S, Weksberg R, Wilson MD, Sedlacek Z, Gagnon C, Musova Z, Chitayat D, Shannon P, Mathieu J, Sermon K, Pearson CE. CpG Methylation, a Parent-of-Origin Effect for Maternal-Biased Transmission of Congenital Myotonic Dystrophy. Am J Hum Genet 2017; 100:488-505. [PMID: 28257691 PMCID: PMC5339342 DOI: 10.1016/j.ajhg.2017.01.033] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 01/26/2017] [Indexed: 12/13/2022] Open
Abstract
CTG repeat expansions in DMPK cause myotonic dystrophy (DM1) with a continuum of severity and ages of onset. Congenital DM1 (CDM1), the most severe form, presents distinct clinical features, large expansions, and almost exclusive maternal transmission. The correlation between CDM1 and expansion size is not absolute, suggesting contributions of other factors. We determined CpG methylation flanking the CTG repeat in 79 blood samples from 20 CDM1-affected individuals; 21, 27, and 11 individuals with DM1 but not CDM1 (henceforth non-CDM1) with maternal, paternal, and unknown inheritance; and collections of maternally and paternally derived chorionic villus samples (7 CVSs) and human embryonic stem cells (4 hESCs). All but two CDM1-affected individuals showed high levels of methylation upstream and downstream of the repeat, greater than non-CDM1 individuals (p = 7.04958 × 10−12). Most non-CDM1 individuals were devoid of methylation, where one in six showed downstream methylation. Only two non-CDM1 individuals showed upstream methylation, and these were maternally derived childhood onset, suggesting a continuum of methylation with age of onset. Only maternally derived hESCs and CVSs showed upstream methylation. In contrast, paternally derived samples (27 blood samples, 3 CVSs, and 2 hESCs) never showed upstream methylation. CTG tract length did not strictly correlate with CDM1 or methylation. Thus, methylation patterns flanking the CTG repeat are stronger indicators of CDM1 than repeat size. Spermatogonia with upstream methylation may not survive due to methylation-induced reduced expression of the adjacent SIX5, thereby protecting DM1-affected fathers from having CDM1-affected children. Thus, DMPK methylation may account for the maternal bias for CDM1 transmission, larger maternal CTG expansions, age of onset, and clinical continuum, and may serve as a diagnostic indicator.
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Abstract
Myotonic dystrophies (dystrophia myotonica, or DM) are inherited disorders characterized by myotonia and progressive muscle degeneration, which are variably associated with a multisystemic phenotype. To date, two types of myotonic dystrophy, type 1 (DM1) and type 2 (DM2), are known to exist; both are autosomal dominant disorders caused by expansion of an untranslated short tandem repeat DNA sequence (CTG)(n) and (CCTG)(n), respectively. These expanded repeats in DM1 and DM2 show different patterns of repeat-size instability. Phenotypes of DM1 and DM2 are similar but there are some important differences, most conspicuously in the severity of the disease (including the presence or absence of the congenital form), muscles primarily affected (distal versus proximal), involved muscle fiber types (type 1 versus type 2 fibers), and some associated multisystemic phenotypes. The pathogenic mechanism of DM1 and DM2 is thought to be mediated by the mutant RNA transcripts containing expanded CUG and CCUG repeats. Strong evidence supports the hypothesis that sequestration of muscle-blind like (MBNL) proteins by these expanded repeats leads to misregulated splicing of many gene transcripts in corroboration with the raised level of CUG-binding protein 1. However, additional mechanisms, such as changes in the chromatin structure involving CTCN-binding site and gene expression dysregulations, are emerging. Although treatment of DM1 and DM2 is currently limited to supportive therapies, new therapeutic approaches based on pathogenic mechanisms may become feasible in the near future.
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Affiliation(s)
- Tetsuo Ashizawa
- Department of Neurology, McKnight Brain Institute, The University of Texas Medical Branch, Galveston, TX, USA.
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Radvansky J, Kadasi L. The expanding world of myotonic dystrophies: how can they be detected? Genet Test Mol Biomarkers 2010; 14:733-41. [PMID: 20939737 DOI: 10.1089/gtmb.2010.0073] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Myotonic dystrophy (DM) comprises at least two genetically distinct forms, both of which are caused by expansions of microsatellite repeats. The expansion of a CTG repeat in the DMPK gene leads to the first genetic form (DM type 1), and the expansion of a CCTG repeat in the ZNF9 gene causes the second genetic form of the disease (DM type 2). In both cases, the repeat units may expand to several thousand repeats, and the number of repeats in the expanded alleles shows a high degree of meiotic and somatic instability. The unprecedented size of expansions and their dynamic nature still represents a diagnostic challenge, which has been facilitated using different methods and modifications since the identification of the underlying mutations of these disorders. Here, we present an overview of the basic methods described for the purpose of identification of the DM type 1 and DM type 2 expansions and discuss particular modifications and improvements implemented to extend the detection ranges of these methods. Our review focuses on the advantages and disadvantages of the methods based on Southern blot analysis, polymerase chain reaction amplification, and in situ hybridization techniques and also on the possibilities of preimplantation and prenatal genetic testing.
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Affiliation(s)
- Jan Radvansky
- Department of Molecular Biology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia Republic.
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6
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Kongenitale myotone Dystrophie. Monatsschr Kinderheilkd 2005. [DOI: 10.1007/s00112-003-0862-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Barber M, Eguiluz I, Plasencia W, Ramírez O. Distrofia miotónica de steinert y gestación. CLINICA E INVESTIGACION EN GINECOLOGIA Y OBSTETRICIA 2003. [DOI: 10.1016/s0210-573x(03)77257-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Piyamongkol W, Harper JC, Sherlock JK, Doshi A, Serhal PF, Delhanty JD, Wells D. A successful strategy for preimplantation genetic diagnosis of myotonic dystrophy using multiplex fluorescent PCR. Prenat Diagn 2001; 21:223-32. [PMID: 11260612 DOI: 10.1002/1097-0223(200103)21:3<223::aid-pd52>3.0.co;2-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The most common form of inherited muscular dystrophy in adults is myotonic dystrophy (DM), an autosomal-dominant disease caused by the expansion of an unstable CTG repeat sequence in the 3' untranslated region of the myotonin protein kinase (DMPK) gene. Expanded (mutant) CTG repeat sequences are refractory to conventional PCR, but alleles with a number of repeats within the normal range can be readily amplified and detected. Preimplantation genetic diagnosis (PGD) of DM has been successfully applied. However, a misdiagnosis using the reported protocol was recently documented. Two new PGD protocols for DM have been developed which utilise multiplex fluorescent PCR. Ideally a linked polymorphic marker, APOC2, is amplified in addition to the normal DMPK alleles, thus providing a back-up diagnostic result. However, the two couples reported in the present study were not fully informative at the APOC2 locus and so an unlinked short tandem repeat (STR) marker, D21S1414, was substituted. The highly polymorphic nature of the D21S1414, DMPK and APOC2 loci means that a very simple genetic fingerprint can be generated by analyses of these loci. This allows most DNA contaminants to be detected. Contamination is a significant problem for PGD and is the primary reason for the inclusion of D21S1414 and APOC2 in this protocol. This paper reports the first clinical experience and pregnancies following PGD for DM using a multiplex fluorescent PCR protocol.
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Affiliation(s)
- W Piyamongkol
- UCL Centre for Preimplantation Genetic Diagnosis and the Assisted Conception Unit, Department of Obstetrics & Gynaecology, University College London, 86-96 Chenies Mews, London WC1E 6HX, UK
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9
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Keriakos R, Aziz N, Sidra L. Myotonic dystrophy in pregnancy. J OBSTET GYNAECOL 1999; 19:71-3. [PMID: 15512229 DOI: 10.1080/01443619966038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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10
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Geifman-Holtzman O, Fay K. Prenatal diagnosis of congenital myotonic dystrophy and counseling of the pregnant mother: Case report and literature review. ACTA ACUST UNITED AC 1998. [DOI: 10.1002/(sici)1096-8628(19980707)78:3<250::aid-ajmg8>3.0.co;2-t] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Wong LJ, Ashizawa T. Instability of the (CTG)n repeat in congenital myotonic dystrophy. Am J Hum Genet 1997; 61:1445-8. [PMID: 9399912 PMCID: PMC1716094 DOI: 10.1086/301654] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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13
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Erikson A, Forsberg H, Drugge U, Holmgren G. Outcome of pregnancy in women with myotonic dystrophy and analysis of CTG gene expansion. Acta Paediatr 1995; 84:416-8. [PMID: 7795352 DOI: 10.1111/j.1651-2227.1995.tb13662.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Pregnancy outcome was investigated in 32 women with clinically obvious myotonic dystrophy. The results indicated that there are two groups of women, those whose children have the adult type of myotonic dystrophy and those whose children have the congenital type. The overall perinatal mortality was 14%. Polyhydramnios was an obvious sign of the congenital type. No subclinical gene carrier was found among the children. We conclude that prenatal diagnosis should be offered to women with myotonic dystrophy, particularly to those who have previously given birth to a child with the congenital type.
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Affiliation(s)
- A Erikson
- Department of Paediatrics, County Hospital, Boden, Sweden
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14
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Reed UC, Passos-Bueno MR, Nagahashi-Marie SK, Cerqueira A, Mendonça LI, Levy JA, Diament A, Zatz M. [Myotonic dystrophy: study of clinico-genetic correlation in a pair of relatives (father-son)]. ARQUIVOS DE NEURO-PSIQUIATRIA 1994; 52:545-8. [PMID: 7611950 DOI: 10.1590/s0004-282x1994000400015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We report the case of a child with myotonic dystrophy (DM) with symptoms beginning at the age of seven, whose genetic study showed an additional DNA fragment, greater than of his father, an asymptomatic carrier. The clinical and molecular analysis of this parent-child pair are probably the first described in Brazil, since the recent discovery of genetic abnormality in DM by American and European researchers, that explained the long-debated phenomenon of "anticipation" in this disease. The main advances in molecular genetics in DM and its correlation with increasing severity and earlier onset of the symptoms in successive generations of a family are commented briefly.
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Affiliation(s)
- U C Reed
- Estudo da Clínica Neurológica (CN) da Faculdade de Medicina (FM) da Universidade de São Paulo, Brasil
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16
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Müller U, Graeber MB, Haberhausen G, Köhler A. Molecular basis and diagnosis of neurogenetic disorders. J Neurol Sci 1994; 124:119-40. [PMID: 7964863 DOI: 10.1016/0022-510x(94)90318-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Over the past few years, molecular neurogenetics has developed into one of the most promising and active research fields. The new discipline applies modern molecular genetic techniques to the investigation of classical neurological disorders. In the following article, a definition of neurogenetic disease is introduced, the molecular basis of four groups of neurogenetic disorders is described and recent diagnostic developments are presented. The first group of diseases is caused by trinucleotide expansions. "Expanding" trinucleotide repeats were not known to occur in any species until about three years ago. Today, disorders such as Huntington's disease, spinocerebellar ataxia type 1, fragile X mental retardation, spinobulbar muscular atrophy and myotonic dystrophy are all known to be caused by the expansion of trinucleotides. The second group is characterized by chromosomal deletions or uniparental disomies. Lissencephaly and the Miller-Dieker syndrome, Prader-Willi and Angelman syndromes and Duchenne and Becker muscular dystrophies belong to this category. The third group includes those neurogenetic disorders that are mainly caused by point mutations such as the X-linked leukodystrophies, including Pelizaeus-Merzbacher disease and adrenoleukodystrophy, Charcot-Marie-Tooth syndrome type 1, familial forms of amyotrophic lateral sclerosis, several types of craniosynostoses and some CNS tumor syndromes. Finally, Alzheimer's and Parkinson's disease are discussed as representatives of group four, i.e. genetically heterogeneous neurological disorders.
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Affiliation(s)
- U Müller
- Institut für Humangenetik, Justus-Liebig-Universität, Giessen, Germany
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Hecht BK, Donnelly A, Gedeon AK, Byard RW, Haan EA, Mulley JC. Direct molecular diagnosis of myotonic dystrophy. Clin Genet 1993; 43:276-85. [PMID: 8370146 DOI: 10.1111/j.1399-0004.1993.tb03819.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Myotonic dystrophy (DM) arises from an unstable trinucleotide (CTGn) repeat sequence within the DM locus at 19q13.3. Twenty-three myotonic dystrophy families containing 205 persons with no symptoms, minimal manifestations, classic DM or congenital DM were investigated to validate the application of the pM10M6 probe to direct molecular diagnosis. Affected family members had been diagnosed clinically and the unaffected family members had been assigned carrier probabilities close to either zero or 100%, using closely linked flanking markers. Southern analysis identified all 89 DM gene carriers as having expansions of the unstable element. PstI detected all small expansions of the repeat sequence as easily seen discrete bands; but large expansions were usually seen as diffuse smears, sometimes difficult to distinguish from lane background. EcoRI concentrated these diffuse smears, associated with somatic instability, into discrete bands which were easy to detect; but it did not resolve the smaller expansions present in 9 (10%) of the DM carriers. It is essential that PstI and EcoRI gels are run in parallel to detect all DM gene carriers. The extent of expansion of CTG correlated with age of onset and disease severity. Biopsies of various fetal tissues from two terminated pregnancies confirmed the diagnosis obtained by CVS and revealed no heterogeneity between tissues at this developmental stage. Further expansion occurred during the culture of CVS cells, indicating that direct prenatal diagnosis needs to be carried out on CVS tissue rather than on cultured cells. The intergenerational change of the repeat sequence from DM parent to DM offspring showed a significant parental sex difference for those parents with large expansions. Contraction of the unstable element was observed in the three males carrying the largest expansions and could explain why congenital DM is exclusively of maternal origin.
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Affiliation(s)
- B K Hecht
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, Australia
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Novelli G, Gennarelli M, Fattorini C, Abbruzzese C, Dallapiccola B. The dynamic genomics of myotonic dystrophy and its clinical relevance: an overview. Biomed Pharmacother 1993; 47:321-30. [PMID: 8061254 DOI: 10.1016/0753-3322(93)90081-u] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Affiliation(s)
- G Novelli
- Cattedra di Genetica Umana Università Cattolica di Roma, Italy
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Suthers GK, Huson SM, Davies KE. Instability versus predictability: the molecular diagnosis of myotonic dystrophy. J Med Genet 1992; 29:761-5. [PMID: 1453422 PMCID: PMC1016166 DOI: 10.1136/jmg.29.11.761] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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