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Dulski J, Sulek A, Krygier M, Radziwonik W, Slawek J. False-negative tests in Huntington's disease: A new variant within primer hybridization site. Eur J Neurol 2021; 28:2103-2105. [PMID: 33576024 DOI: 10.1111/ene.14772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 02/02/2021] [Accepted: 02/04/2021] [Indexed: 11/29/2022]
Abstract
BACKGROUND Establishing the diagnosis of Huntington's disease (HD) involves molecular genetic testing and estimation of the number of CAG repeats. MATERIAL AND METHODS We report a 42-year-old patient with clinical phenotype suggestive of HD, who was repeatedly negative on genetic testing for HD at a reference laboratory. He had positive history of similar symptoms in his father, but not in other family members. During a 2-year follow-up his symptoms slowly deteriorated (videos attached). The family history was misleading, as we discovered that patient's father was adopted as infant. Having excluded HD-like disorders and other causes of the symptoms we hypothesized that the primer could not bind to the mutated allele. RESULTS The PCR reaction with primers HD1 and Hu3 revealed homozygosity of the other adjacent microsatellite tract consisting of the CCG repeats. The newly designed set of primers, located outside of the CAG tract (HD6extF, HD7extR) was used and enabled amplification of the mutant allele and detection of the abnormal range of CAG repeats. CONCLUSIONS As application of the novel primers led to the diagnosis of HD in other 5 patients previously tested negative, we propose their incorporation into routine genetic testing in patients suspected of HD displaying homoallelism in the standard protocol.
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Affiliation(s)
- Jaroslaw Dulski
- Department of Neurological and Psychiatric Nursing, Faculty of Health Sciences, Medical University of Gdansk, Gdansk, Poland.,Neurology Department, St Adalbert Hospital, Copernicus PL, Gdansk, Poland
| | - Anna Sulek
- Department of Genetics, Institute of Psychiatry and Neurology, Warsaw, Poland
| | - Magdalena Krygier
- Department of Developmental Neurology, University Clinical Centre, Medical University of Gdansk, Gdansk, Poland
| | - Wiktoria Radziwonik
- Department of Genetics, Institute of Psychiatry and Neurology, Warsaw, Poland
| | - Jaroslaw Slawek
- Department of Neurological and Psychiatric Nursing, Faculty of Health Sciences, Medical University of Gdansk, Gdansk, Poland.,Neurology Department, St Adalbert Hospital, Copernicus PL, Gdansk, Poland
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Magri S, Nanetti L, Mongelli A, Rizzo E, Taroni F, Mariotti C, Gellera C. Missing the pathological expansion in Huntington disease: de novo c.51C>G variant on the expanded allele causing intrafamilial allele dropout. Am J Med Genet A 2020; 185:397-400. [PMID: 33247537 DOI: 10.1002/ajmg.a.61973] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 10/08/2020] [Accepted: 10/25/2020] [Indexed: 11/08/2022]
Abstract
Huntington disease (HD) is an autosomal dominant disease characterized by motor, behavioral, and cognitive symptoms, caused by the pathological expansion of more than 35 CAG/CAA repeats in the HTT gene. We describe the phenotype of a patient compatible with HD. Several family members were reported as affected, and a paternal cousin and his daughter carried 39 and 42 CAG/CAA. HD genetic testing in proband showed homozygosity for a 14 CAG/CAA allele. Considering the phenotype and family history, HTT gene sequence was performed, revealing heterozygosity for the c.51C>G variant that changes the last nucleotide before the CAG tract, causing misannealing of forward primer (HD344) and dropout of the expanded allele. Polymerase chain reaction (PCR) analysis performed with an alternative forward primer demonstrated a 41 CAG/CAA allele. The c.51C>G variant was not detected in the affected cousin, thus suggesting a de novo occurrence. The lack of biological samples from the proband father and grandmother prevented further investigations to establish in which family member the variant occurred. These data indicate that patients presenting HD phenotype, and homozygous for a normal HTT CAG/CAA allele should be thoroughly evaluated for the presence of a genetic variant, even de novo, within the repeat region that may hamper genetic diagnosis.
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Affiliation(s)
- Stefania Magri
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Lorenzo Nanetti
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Alessia Mongelli
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Elena Rizzo
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Franco Taroni
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Caterina Mariotti
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Cinzia Gellera
- Unit of Medical Genetics and Neurogenetics, Department of Diagnostics and Technology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
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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] [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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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] [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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Levin BC, Richie KL, Jakupciak JP. Advances in Huntington’s disease diagnostics: development of a standard reference material. Expert Rev Mol Diagn 2014; 6:587-96. [PMID: 16824032 DOI: 10.1586/14737159.6.4.587] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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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Losekoot M, van Belzen MJ, Seneca S, Bauer P, Stenhouse SAR, Barton DE. EMQN/CMGS best practice guidelines for the molecular genetic testing of Huntington disease. Eur J Hum Genet 2013; 21:480-6. [PMID: 22990145 PMCID: PMC3641377 DOI: 10.1038/ejhg.2012.200] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Huntington disease (HD) is caused by the expansion of an unstable polymorphic trinucleotide (CAG)n repeat in exon 1 of the HTT gene, which translates into an extended polyglutamine tract in the protein. Laboratory diagnosis of HD involves estimation of the number of CAG repeats. Molecular genetic testing for HD is offered in a wide range of laboratories both within and outside the European community. In order to measure the quality and raise the standard of molecular genetic testing in these laboratories, the European Molecular Genetics Quality Network has organized a yearly external quality assessment (EQA) scheme for molecular genetic testing of HD for over 10 years. EQA compares a laboratory's output with a fixed standard both for genotyping and reporting of the results to the referring physicians. In general, the standard of genotyping is very high but the clarity of interpretation and reporting of the test result varies more widely. This emphasizes the need for best practice guidelines for this disorder. We have therefore developed these best practice guidelines for genetic testing for HD to assist in testing and reporting of results. The analytical methods and the potential pitfalls of molecular genetic testing are highlighted and the implications of the different test outcomes for the consultand and his or her family members are discussed.
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Affiliation(s)
- Monique Losekoot
- Department of Clinical Genetics, Laboratory for Diagnostic Genome Analysis, Leiden University Medical Centre, Leiden, The Netherlands.
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Jama M, Millson A, Miller CE, Lyon E. Triplet repeat primed PCR simplifies testing for Huntington disease. J Mol Diagn 2013; 15:255-62. [PMID: 23414820 DOI: 10.1016/j.jmoldx.2012.09.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 09/18/2012] [Accepted: 09/26/2012] [Indexed: 12/14/2022] Open
Abstract
Diagnostic and predictive testing for Huntington disease (HD) requires an accurate determination of the number of CAG repeats in the Huntingtin (HHT) gene. Currently, when a sample appears to be homozygous for a normal allele, additional testing is required to confirm amplification from both alleles. If the sample still appears homozygous, Southern blot analysis is performed to rule out an undetected expanded HTT allele. Southern blot analysis is expensive, time-consuming, and labor intensive and requires high concentrations of DNA. We have developed a chimeric PCR process to help streamline workflow; true homozygous alleles are easily distinguished by this simplified method, and only very large expanded alleles still require Southern blot analysis. Two hundred forty-six HD samples, previously run with a different fragment analysis method, were analyzed with our new method. All samples were correctly genotyped, resulting in 100% concordance between the methods. The chimeric PCR assay was able to identify expanded alleles up to >150 CAG repeats. This method offers a simple strategy to differentiate normal from expanded CAG alleles, thereby reducing the number of samples reflexed to Southern blot analysis. It also provides assurance that expanded alleles are not routinely missed because of allele dropout.
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Affiliation(s)
- Mohamed Jama
- ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah 84108, USA.
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Blanco S, Suarez A, Gandia-Pla S, Gómez-Llorente C, Antúnez A, Gómez-Capilla JA, Fárez-Vidal ME. Use of capillary electrophoresis for accurate determination of CAG repeats causing Huntington disease. An oligonucleotide design avoiding shadow bands. Scandinavian Journal of Clinical and Laboratory Investigation 2009; 68:577-84. [PMID: 19378429 DOI: 10.1080/00365510801915171] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Huntington disease (HD) is a neurodegenerative disorder associated with the expansion of a polymorphic trinucleotide CAG repeat in the HD gene. We have developed an assay to accurately determine CAG repeats that combines a novel oligonucleotide design and the resolution of capillary electrophoresis. A mismatch in the second nucleotide from the 3' end enhanced specificity by avoiding mispriming and diminishing shadow bands and artifactual PCR products. The coupling of capillary electrophoresis analysis with the assay added the advantages of accuracy, high resolution, semi-automation, rapid analysis and low sample consumption. Analysis of 200 chromosomes in the Spanish population sample studied (control group) gave a peak frequency for 16 CAG repeats and of 7 triplets for CCG repeats. Diagnosis of HD was confirmed in 22 of 34 individuals with a range of CAG repeats from 39 to 52. Predictive testing was also carried out for 19 relatives of the HD families diagnosed at our laboratory. The method proposed in this article provides an accurate sizing of DNA repeats that can be applied to the analysis of DNA size-related disorders.
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Affiliation(s)
- Sonia Blanco
- Departamento de Bioquímica y Biología Molecular, Universidad de Granada, Spain
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Allen RA, Gatalica Z, Knezetic J, Hatcher L, Vogel JS, Dunn ST. A common 1317TC polymorphism in MTHFR can lead to erroneous 1298AC genotyping by PCR-RE and TaqMan probe assays. ACTA ACUST UNITED AC 2007; 11:167-73. [PMID: 17627388 DOI: 10.1089/gte.2006.0513] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Multiple polymorphisms of the methylenetetrahydrofolate reductase gene (MTHFR) have been documented, and some are associated with decreased enzyme activity. One polymorphism, 677CT, is commonly tested in the context of thrombosis. Recently, consideration has also been extended to 1298AC, which is also associated with reduced catalytic activity. This report describes problems arising during the development of a PCR restriction enzyme assay for 1298AC. In the process of validating a PCR-MboII assay, it was realized that a nearby 1317TC polymorphism rendered a restriction fragment length polymorphism (RFLP) pattern that was virtually indistinguishable from a 1298A allele. An alternate approach, involving primer mutagenesis and Fnu4HI digestion, resolved the problem. To validate the latter assay, samples were obtained from a CLIA-approved facility that had developed a multiplexed real-time PCR using TaqMan probes for simultaneous assessment of 677CT and 1298AC. Interlaboratory results concurred for 10 out of 11 samples; however, one sample was consistently heterozygous by PCR-Fnu4HI and homozygous 1298CC by real-time PCR. Bidirectional sequencing confirmed that the sample was a compound 1298AC/1317TC heterozygote. It is likely that the 1317C variant, residing with 1298A on one chromosome, disrupted primer annealing in the TaqMan assay, leading to preferential amplification of the 1298C/1317T chromosome and hence an aberrant homozygous 1298CC genotype. This validation exercise emphasizes the need for comprehensive appraisal and continual reassessment of the optimal performance of molecular diagnostic assays. It is hoped that laboratories offering MTHFR 1298AC testing are cognizant of some of the inherent problems in published methods.
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Affiliation(s)
- Richard A Allen
- Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
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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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Abstract
BACKGROUND Huntington disease (HD) is a rare, progressive, and fatal autosomal dominant neurodegenerative disorder, typically of adult onset. METHODS We reviewed the literature concerning the molecular diagnosis of HD. RESULTS The discovery of the genetic etiology of HD, a trinucleotide expansion mutation on chromosome 4p, has led to the development of increasingly reliable and valid diagnostic tests that can be applied to symptomatic patients, individuals at risk for HD but currently asymptomatic, fetuses, and embryos. However, the unstable nature of the HD mutation, the lack of effective treatments for HD, the mid-adulthood age of disease onset, and the existence of disorders with the same clinical presentation but different etiology all complicates diagnostic testing. CONCLUSION Conscientious laboratory work, knowledgeable interpretation of genetic test results, and the availability of pre- and posttest counseling are essential components of HD diagnosis.
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Affiliation(s)
- Russell L Margolis
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
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Jeffrey GP, Adams PC. Pitfalls in the genetic diagnosis of hereditary hemochromatosis. GENETIC TESTING 2001; 4:143-6. [PMID: 10953953 DOI: 10.1089/10906570050114849] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The widespread use of the genotype assay that identifies the common C282Y mutation in the HFE gene has allowed an earlier diagnosis to be made in many subjects. A significant number of these patients may have no evidence of phenotypic disease and have a normal serum ferritin level. This phenomenon is more common when the genotype assay is used to screen populations rather than higher-risk groups such as family members of a proband with hereditary hemochromatosis. Moreover, patients with significant iron overload may be wild type for the C282Y mutation and have no other demonstrable mutation of the HFE gene. The HFE genotype assay has recently been found to give a false-positive C282Y homozygous result in half of the subjects in one population screening study due to the presence of a single nucleotide polymorphism (SNP) that interfered with primer binding in the PCR assay. The problem may be overcome by using alternate primers. A number of other groups have confirmed the finding but in a much smaller number of subjects, whereas others found that their assays were not affected by the SNP. The use of the HFE genotype assay as the sole diagnostic criterion for hereditary hemochromatosis is not recommended. The genotype assay should be used as an adjunct to the established methods of demonstrating iron overload and be viewed as a predictor of either the presence of iron overload or the subsequent development of iron overload during an individual's lifetime.
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Affiliation(s)
- G P Jeffrey
- Faculty of Medicine and Dentistry, University of Western Australia, and Sir Charles Gairdner Hospital, Nedlands, Perth.
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Yu S, Fimmel A, Fung D, Trent RJ. Polymorphisms in the CAG repeat--a source of error in Huntington disease DNA testing. Clin Genet 2000; 58:469-72. [PMID: 11149616 DOI: 10.1034/j.1399-0004.2000.580607.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Five of 400 patients (1.3%), referred for Huntington disease DNA testing, demonstrated a single allele on CAG alone, but two alleles when the CAG + CCG repeats were measured. The PCR assay failed to detect one allele in the CAG alone assay because of single-base silent polymorphisms in the penultimate or the last CAG repeat. The region around and within the CAG repeat sequence in the Huntington disease gene is a hot-spot for DNA polymorphisms, which can occur in up to 1% of subjects tested for Huntington disease. These polymorphisms may interfere with amplification by PCR, and so have the potential to produce a diagnostic error.
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Affiliation(s)
- S Yu
- Department of Molecular and Clinical Genetics, Royal Prince Alfred Hospital, Camperdown NSW, Australia
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