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PerezGrovas-Saltijeral A, Ochoa-Morales A, Jara-Prado A, Velázquez-Cruz R, Rivera-Paredez B, Dávila-OrtizdeMontellano D, Benítez-Alonso EO, Santamaría-Olmedo M, Sevilla-Montoya R, Marfil-Marín E, Valdés-Flores M, Martínez-Ruano L, Camacho-Molina A, Hidalgo-Bravo A. Unraveling the role of relative telomere length and CAG expansion on initial symptoms of juvenile Huntington disease. Eur J Neurol 2023; 30:612-621. [PMID: 36421025 DOI: 10.1111/ene.15644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Accepted: 11/21/2022] [Indexed: 11/25/2022]
Abstract
BACKGROUND AND PURPOSE Juvenile-onset Huntington disease (JHD) is defined when symptoms initiate before 20 years of age. Mechanisms explaining differences between juvenile and adult onset are not fully understood. Our aim was to analyze the distribution of initial symptoms in a cohort of JHD patients and to explore its relationship with CAG expansion and relative telomere length (RTL). METHODS A total of 84 JHD patients and 54 neurologically healthy age and sex matched individuals were recruited. CAG length was measured by southern blot or triplet repeat primed polymerase chain reaction. RTL was measured using the Cawthon method. RESULTS Psychiatric symptoms were most frequent when considering the entire cohort. When divided into onset before or after 10 years, cognitive symptoms were more frequent in the youngest, whilst in the older group psychiatric symptoms prevailed. Motor symptoms were rare in the youngest and epilepsy was observed only in this group as well as a larger CAG expansion. RTL analysis revealed shorter telomeres in JHD patients compared to controls. This difference is not influenced by age, initial symptoms, time of disease or CAG expansion. CONCLUSIONS To the best of our knowledge this is the largest cohort of JHD patients reported. Psychiatric manifestations deserve special attention when JHD is suspected and epilepsy is especially important in the youngest patients. Initial symptoms seem to be influenced by CAG expansion and therefore age of onset. RTL is significantly reduced in JHD patients which can influence the characteristic neurodegeneration of JHD and contribute to the clinical discrepancy between adult and juvenile forms of Huntington disease.
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Affiliation(s)
| | - Adriana Ochoa-Morales
- Department of Neurogenetics, National Institute of Neurology and Neurosurgery, Mexico City, Mexico
| | - Aurelio Jara-Prado
- Department of Neurogenetics, National Institute of Neurology and Neurosurgery, Mexico City, Mexico
| | - Rafael Velázquez-Cruz
- Genomics of Bone Metabolism Laboratory, National Institute of Genomic Medicine (INMEGEN), Mexico City, Mexico
| | - Berenice Rivera-Paredez
- Research Center in Policies, Population and Health, School of Medicine, National Autonomous University of Mexico (UNAM), Mexico City, Mexico
| | | | - Edmar O Benítez-Alonso
- Department of Neurogenetics, National Institute of Neurology and Neurosurgery, Mexico City, Mexico
| | | | - Rosalba Sevilla-Montoya
- Department of Genetics and Human Genomics, National Institute of Perinatology, Mexico City, Mexico
| | | | | | - Leticia Martínez-Ruano
- Department of Neurogenetics, National Institute of Neurology and Neurosurgery, Mexico City, Mexico
| | - Alejandra Camacho-Molina
- Department of Neurogenetics, National Institute of Neurology and Neurosurgery, Mexico City, Mexico
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De Luca A, Morella A, Consoli F, Fanelli S, Thibert JR, Statt S, Latham GJ, Squitieri F. A Novel Triplet-Primed PCR Assay to Detect the Full Range of Trinucleotide CAG Repeats in the Huntingtin Gene ( HTT). Int J Mol Sci 2021; 22:ijms22041689. [PMID: 33567536 PMCID: PMC7916029 DOI: 10.3390/ijms22041689] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Revised: 02/04/2021] [Accepted: 02/04/2021] [Indexed: 02/07/2023] Open
Abstract
The expanded CAG repeat number in HTT gene causes Huntington disease (HD), which is a severe, dominant neurodegenerative illness. The accurate determination of the expanded allele size is crucial to confirm the genetic status in symptomatic and presymptomatic at-risk subjects and avoid genetic polymorphism-related false-negative diagnoses. Precise CAG repeat number determination is critical to discriminate the cutoff between unexpanded and intermediate mutable alleles (IAs, 27–35 CAG) as well as between IAs and pathological, low-penetrance alleles (i.e., 36–39 CAG repeats), and it is also critical to detect large repeat expansions causing pediatric HD variants. We analyzed the HTT-CAG repeat number of 14 DNA reference materials and of a DNA collection of 43 additional samples carrying unexpanded, IAs, low and complete penetrance alleles, including large (>60 repeats) and very large (>100 repeats) expansions using a novel triplet-primed PCR-based assay, the AmplideX PCR/CE HTT Kit. The results demonstrate that the method accurately genotypes both normal and expanded HTT-CAG repeat numbers and reveals previously undisclosed and very large CAG expansions >200 repeats. We also show that this technique can improve genetic test reliability and accuracy by detecting CAG expansions in samples with sequence variations within or adjacent to the repeat tract that cause allele drop-outs or inaccuracies using other PCR methods.
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Affiliation(s)
- Alessandro De Luca
- Medical Genetics Division, Fondazione IRCCS Casa Sollievo della Sofferenza, 71013 San Giovanni Rotondo, Italy; (A.D.L.); (A.M.); (F.C.)
| | - Annunziata Morella
- Medical Genetics Division, Fondazione IRCCS Casa Sollievo della Sofferenza, 71013 San Giovanni Rotondo, Italy; (A.D.L.); (A.M.); (F.C.)
| | - Federica Consoli
- Medical Genetics Division, Fondazione IRCCS Casa Sollievo della Sofferenza, 71013 San Giovanni Rotondo, Italy; (A.D.L.); (A.M.); (F.C.)
| | - Sergio Fanelli
- Huntington and Rare Diseases Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, 71013 San Giovanni Rotondo, Italy;
| | - Julie R. Thibert
- Asuragen, Inc., Austin, TX 78744, USA; (J.R.T.); (S.S.); (G.J.L.)
| | - Sarah Statt
- Asuragen, Inc., Austin, TX 78744, USA; (J.R.T.); (S.S.); (G.J.L.)
| | - Gary J. Latham
- Asuragen, Inc., Austin, TX 78744, USA; (J.R.T.); (S.S.); (G.J.L.)
| | - Ferdinando Squitieri
- Huntington and Rare Diseases Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, 71013 San Giovanni Rotondo, Italy;
- Correspondence: ; Tel.: +39-06-44160536
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PerezGrovas-Saltijeral A, Ochoa-Morales A, Miranda-Duarte A, Martínez-Ruano L, Jara-Prado A, Camacho-Molina A, Hidalgo-Bravo A. Telomere length analysis on leukocytes derived from patients with Huntington Disease. Mech Ageing Dev 2020; 185:111189. [DOI: 10.1016/j.mad.2019.111189] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 10/30/2019] [Accepted: 11/19/2019] [Indexed: 02/03/2023]
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4
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Abstract
Huntington's disease (HD) is caused by a CAG repeat expansion in the HTT gene. Repeat length can change over time, both in individual cells and between generations, and longer repeats may drive pathology. Cellular DNA repair systems have long been implicated in CAG repeat instability but recent genetic evidence from humans linking DNA repair variants to HD onset and progression has reignited interest in this area. The DNA damage response plays an essential role in maintaining genome stability, but may also license repeat expansions in the context of HD. In this chapter we summarize the methods developed to assay CAG repeat expansion/contraction in vitro and in cells, and review the DNA repair genes tested in mouse models of HD. While none of these systems is currently ideal, new technologies, such as long-read DNA sequencing, should improve the sensitivity of assays to assess the effects of DNA repair pathways in HD. Improved assays will be essential precursors to high-throughput testing of small molecules that can alter specific steps in DNA repair pathways and perhaps ameliorate expansion or enhance contraction of the HTT CAG repeat.
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5
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Zhao M, Cheah FSH, Chen M, Lee CG, Law HY, Chong SS. Improved high sensitivity screen for Huntington disease using a one-step triplet-primed PCR and melting curve assay. PLoS One 2017; 12:e0180984. [PMID: 28700716 PMCID: PMC5507316 DOI: 10.1371/journal.pone.0180984] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 05/22/2017] [Indexed: 11/19/2022] Open
Abstract
Molecular diagnosis of Huntington disease (HD) is currently performed by fluorescent repeat-flanking or triplet-primed PCR (TP-PCR) with capillary electrophoresis (CE). However, CE requires multiple post-PCR steps and may result in high cost in high-throughput settings. We previously described a cost-effective single-step molecular screening strategy employing the use of melting curve analysis (MCA). However, because it relies on repeat-flanking PCR, its efficiency in detecting expansion mutations decreases with increasing size of the repeat, which could lead to false-negative results. To address this pitfall, we have developed an improved screening assay coupling TP-PCR, which has been shown in CE-based assays to detect all expanded alleles regardless of size, with MCA in a rapid one-step assay. A companion protocol for rapid size confirmation of expansion-positive samples is also described. The assay was optimized on 30 genotype-known DNAs, and two plasmids pHTT(CAG)26 and pHTT(CAG)33 were used to establish the threshold temperatures (TTs) distinguishing normal from expansion-positive samples. In contrast to repeat-flanking PCR MCA, TP-PCR MCA displayed much higher sensitivity for detecting large expansions. All 30 DNAs generated distinct melt peak Tms which correlated well with each sample's larger allele. Normal samples were clearly distinguished from affected samples. The companion sizing protocol accurately sized even the largest expanded allele of ~180 CAGs. Blinded analysis of 69 clinical samples enriched for HD demonstrated 100% assay sensitivity and specificity in sample segregation. The assay targets the HTT CAG repeat specifically, tolerates a wide range of input DNA, and works well using DNA from saliva and buccal swab in addition to blood. Therefore, rapid, accurate, reliable, and high-throughput detection/exclusion of HD can be achieved using this one-step screening assay, at less than half the cost of fluorescent PCR with CE.
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Affiliation(s)
- Mingjue Zhao
- Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Felicia S. H. Cheah
- Khoo Teck Puat – National University Children’s Medical Institute, National University Health System, Singapore, Singapore
| | - Min Chen
- Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Caroline G. Lee
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- Division of Medical Sciences, National Cancer Center, Singapore, Singapore
- Duke-NUS Graduate Medical School, Singapore, Singapore
| | - Hai-Yang Law
- Department of Pediatric Medicine, KK Women’s and Children’s Hospital, Singapore, Singapore
| | - Samuel S. Chong
- Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- Khoo Teck Puat – National University Children’s Medical Institute, National University Health System, Singapore, Singapore
- Department of Laboratory Medicine, National University Hospital, Singapore, Singapore
- * E-mail:
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6
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Affiliation(s)
- Murat Bastepe
- Neurogenetics DNA Diagnostic Laboratory, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Boston Massachusetts
- Genetics Training Program, Harvard Medical School Boston Massachusetts
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School Boston Massachusetts
| | - Winnie Xin
- Neurogenetics DNA Diagnostic Laboratory, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Boston Massachusetts
- Center for Human Genetic Research, Massachusetts General Hospital and Harvard Medical School Boston Massachusetts
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Bean L, Bayrak-Toydemir P. American College of Medical Genetics and Genomics Standards and Guidelines for Clinical Genetics Laboratories, 2014 edition: technical standards and guidelines for Huntington disease. Genet Med 2014; 16:e2. [PMID: 25356969 DOI: 10.1038/gim.2014.146] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 09/15/2014] [Indexed: 11/09/2022] Open
Abstract
Huntington disease is an autosomal-dominant neurodegenerative disease of mid-life onset caused by expansion of a polymorphic trinucleotide (CAG) repeat. Variable penetrance for alleles carrying 36-39 repeats has been noted, but the disease appears fully penetrant when the repeat numbers are >40. An abnormal CAG repeat may expand, contract, or be stably transmitted when passed from parent to child. Assays used to diagnose Huntington disease must be optimized to ensure the accurate and unambiguous quantitation of CAG repeat length. This document provides an overview of Huntington disease and methodological considerations for Huntington disease testing. Examples of laboratory reports are also included.
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Affiliation(s)
- Lora Bean
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Pinar Bayrak-Toydemir
- Department of Pathology, University of Utah School of Medicine and ARUP Laboratories, Salt Lake City, Utah, USA
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8
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Abstract
Huntington's disease (HD) is a neurodegenerative disease that affects four to seven individuals per 100,000. The onset of symptoms usually begins in middle age, although approximately 5% become symptomatic as juveniles. Death occurs approximately 15 years following the onset of symptoms, which include choreic movements, cognitive decline and psychiatric changes. HD is an autosomal dominant inherited disease that is associated with an expansion of a trinucleotide (CAG) repeat located on chromosome 4. Physicians rely on a positive family history, and diagnostic and genetic tests to detect the expansion in the number of CAG trinucleotide repeats in the HD gene to confirm the diagnosis. More than 99% of HD patients have 40 or more CAG triplet repeats and, therefore, targeted mutational analysis is greater than 99% sensitive. Individuals with 26 triplet repeats or less are normal, and while those with 27-35 repeats may not demonstrate symptoms themselves, their offspring may have the disease. Individuals with 36-39 repeats may or may not exhibit symptoms. The College of American Pathology/American College of Medical Genetics Biochemical and Molecular Genetics Resource Committee has emphasized the need to standardize the methodology for the determination of the accurate number of CAG repeats. This will prevent false-positive or -negative results when conducting predictive or prenatal testing of at-risk individuals. The National Institute of Standards and Technology is developing a standard reference material to provide these positive and negative controls needed by clinical testing laboratories. The use of a HD standard reference material will provide the quality control and assurance that data from different laboratories are both comparable and accurate.
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Affiliation(s)
- Barbara C Levin
- National Institute of Standards & Technology, 100 Bureau Drive, Mail Stop 8311, Biochemical Science Division, Chemical Science & Technology Laboratory, Gaithersburg, MD 20899-8311, USA.
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Costa MDC, Teixeira-Castro A, Constante M, Magalhães M, Magalhães P, Cerqueira J, Vale J, Passão V, Barbosa C, Robalo C, Coutinho P, Barros J, Santos MM, Sequeiros J, Maciel P. Exclusion of mutations in the PRNP, JPH3, TBP, ATN1, CREBBP, POU3F2 and FTL genes as a cause of disease in Portuguese patients with a Huntington-like phenotype. J Hum Genet 2006; 51:645-651. [PMID: 16858508 PMCID: PMC2909272 DOI: 10.1007/s10038-006-0001-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2006] [Accepted: 04/16/2006] [Indexed: 10/24/2022]
Abstract
Huntington disease (HD) is an autosomal dominant neurodegenerative disorder characterised by chorea, cognitive impairment, dementia and personality changes, caused by the expansion of a CAG repeat in the HD gene. Often, patients with a similar clinical presentation do not carry expansions of the CAG repeat in this gene [Huntington disease-like (HDL) patients]. We report the genetic analysis of 107 Portuguese patients with an HDL phenotype. The HDL genes PRNP and JPH3, encoding the prion protein and junctophilin-3, respectively, were screened for repeat expansions in these patients. Given the partial clinical overlap of SCA17, DRPLA and neuroferritinopathy with HD, their causative genes (TBP, ATN1, and FTL, respectively) were also analysed. Finally, repeat expansions in two candidate genes, CREBBP and POU3F2, which encode the nuclear transcriptional coactivator CREB-binding protein and the CNS-specific transcription factor N-Oct-3, respectively, were also studied. Expansions of the repetitive tracts of the PRNP, JPH3, TBP, ATN1, CREBBP and POU3F2 genes were excluded in all patients, as were sequence alterations in the FTL gene. Since none of the genes already included in the differential diagnosis of HD was responsible for the disease in our sample, the genetic heterogeneity of the HDL phenotype is still open for investigation.
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Affiliation(s)
- Maria do Carmo Costa
- Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Andreia Teixeira-Castro
- Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Marco Constante
- Department of Medicine, CHUM, Université de Montreal, Hôpital Notre-Dame, Montreal, Canada
| | | | - Paula Magalhães
- UnIGENe, Institute for Molecular and Cell Biology, Porto, Portugal
| | - Joana Cerqueira
- UnIGENe, Institute for Molecular and Cell Biology, Porto, Portugal
| | - José Vale
- Hospital Egas Moniz, Lisboa, Portugal
| | | | | | | | - Paula Coutinho
- Hospital de São Sebastião, Santa Maria da Feira, Portugal
| | - José Barros
- Hospital Geral de Sto. António, Porto, Portugal
| | - Manuela M Santos
- Department of Medicine, CHUM, Université de Montreal, Hôpital Notre-Dame, Montreal, Canada
- UnIGENe, Institute for Molecular and Cell Biology, Porto, Portugal
| | - Jorge Sequeiros
- UnIGENe, Institute for Molecular and Cell Biology, Porto, Portugal
- Department of Population Studies, ICBAS, University of Porto, Porto, Portugal
| | - Patrícia Maciel
- Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal.
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Abstract
One mission of the ACMG Laboratory Quality Assurance (QA) Committee is to develop standards and guidelines for clinical genetics laboratories, including cytogenetics, biochemical, and molecular genetics specialties. This document was developed under the auspices of the Molecular Subcommittee of the Laboratory QA Committee by the Huntington Disease (HD) Working Group. These guidelines are not to be interpreted as restrictive or the only approach but to provide a helpful guide. Certainly, appropriately trained and credentialed laboratory directors have flexibility to utilize various testing platforms and design testing strategies with considerable latitude. We felt that it was essential to include technique-specific guidelines of several current technologies commonly used in laboratories providing HD testing, because the technologies discussed are available commercially and are widely utilized. We take the view that these technologies may change, and thus this document may change with future review.
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Affiliation(s)
- Nicholas T Potter
- Molecular Subcommittee of the Laboratory Quality Assurance Committee, Huntington Disease Molecular Working Group, and Laboratory Quality Assurance Committee, Bethesda, Maryland, USA
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11
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Costa MDC, Magalhães P, Ferreirinha F, Guimarães L, Januário C, Gaspar I, Loureiro L, Vale J, Garrett C, Regateiro F, Magalhães M, Sousa A, Maciel P, Sequeiros J. Molecular diagnosis of Huntington disease in Portugal: implications for genetic counselling and clinical practice. Eur J Hum Genet 2003; 11:872-8. [PMID: 14571273 DOI: 10.1038/sj.ejhg.5201055] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Huntington disease (HD) is a neurodegenerative, autosomal dominant disorder of late-onset, caused by the expansion of a CAG repeat in the coding region of the gene. Ours is the reference laboratory for genetic testing in HD, in Portugal, since 1998; 90.1% of all 158 families known were identified for the first time, including patients with unusual presentation or without family history. A total of 338 genetic tests were performed: 234 for diagnosis, 96 for presymptomatic and four for prenatal testing (four were done for family studies). Most referring physicians were neurologists (90.6%); 82.8% of all clinical diagnosis were confirmed, while 83.1% of those sent for exclusion were in fact excluded. In presymptomatic testing, an excess of female subjects (59.4%) was again verified; 37.5% of the consultands were found to be carriers. None of the foetuses, in four prenatal tests, were mutation carriers. One juvenile case was inherited from her mother. Our patient population is very similar to others described so far, namely in terms of mean age at onset and (CAG)(n) distribution, except perhaps for a higher frequency of large normal (class 2) alleles (3.7%). We also identify cases posing particular problems for genetic counselling, such as, 'homozygosity' that can pose a serious ethical dilemma, carriers of large normal alleles, and 'homoallelism' for a normal gene, which will demand further procedures and may delay results in presymptomatic and prenatal testing.
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Abstract
Juvenile Huntington's disease (HD) becomes clinically manifest before 20 years of age. The diagnosis of HD is based on family history, characteristic clinical findings, and the detection of an expansion of a CAG polyglutamine tract in the Huntingtin gene. Juvenile HD is characterized by paternal anticipation and large CAG expansions that may be missed using routine molecular analysis. We have developed an easy, rapid, and reliable modified PCR method using XL (Extra Long) PCR that allowed us to diagnose one of the youngest children reported with juvenile HD. Without this innovation we would not have been able to demonstrate the large CAG expansion. This assay could become part of a standard protocol for HD testing in molecular diagnostic laboratories.
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Affiliation(s)
- J M Milunsky
- Center for Human Genetics, Boston University School of Medicine, Boston, MA 02118, USA.
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Williams LC, Hegde MR, Nagappan R, Faull RL, Giles J, Winship I, Snow K, Love DR. Null alleles at the Huntington disease locus: implications for diagnostics and CAG repeat instability. Genet Test 2000; 4:55-60. [PMID: 10794362 DOI: 10.1089/109065700316480] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PCR amplification of the CAG repeat in exon 1 of the IT15 gene is routinely undertaken to confirm a clinical diagnosis of Huntington disease (HD) and to provide predictive testing for at-risk relatives of affected individuals. Our studies have detected null alleles on the chromosome carrying the expanded repeat in three of 91 apparently unrelated HD families. Sequence analysis of these alleles has revealed the same mutation event, leading to the juxtaposition of uninterrupted CAG and CCG repeats. These data suggest that a mutation-prone region exists in the IT15 gene bounded by the CAG and CCG repeats and that caution should be exercised in designing primers that anneal to the region bounded by these repeats. Two of the HD families segregated null alleles with expanded uninterrupted CAG repeats at the lower end of the zone of reduced penetrance. The expanded repeats are meiotically unstable in these families, although this instability is within a small range of repeat lengths. The haplotypes of the disease-causing chromosomes in these two families differ, only one of which is similar to that reported previously as being specific for new HD mutations. Finally, no apparent mitotic instability of the uninterrupted CAG repeat was observed in the brain of one of the HD individuals.
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Affiliation(s)
- L C Williams
- School of Biological Sciences, University of Auckland, New Zealand
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14
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Nance MA, Seltzer W, Ashizawa T, Bennett R, McIntosh N, Myers RH, Potter NT, Shea DK. Laboratory Guidelines for Huntington Disease Genetic Testing. Am J Hum Genet 1998. [DOI: 10.1086/301846] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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