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Alfano M, De Antoni L, Centofanti F, Visconti VV, Maestri S, Degli Esposti C, Massa R, D'Apice MR, Novelli G, Delledonne M, Botta A, Rossato M. Characterization of full-length CNBP expanded alleles in myotonic dystrophy type 2 patients by Cas9-mediated enrichment and nanopore sequencing. eLife 2022; 11:80229. [PMID: 36018009 PMCID: PMC9462847 DOI: 10.7554/elife.80229] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 08/25/2022] [Indexed: 11/30/2022] Open
Abstract
Myotonic dystrophy type 2 (DM2) is caused by CCTG repeat expansions in the CNBP gene, comprising 75 to >11,000 units and featuring extensive mosaicism, making it challenging to sequence fully expanded alleles. To overcome these limitations, we used PCR-free Cas9-mediated nanopore sequencing to characterize CNBP repeat expansions at the single-nucleotide level in nine DM2 patients. The length of normal and expanded alleles can be assessed precisely using this strategy, agreeing with traditional methods, and revealing the degree of mosaicism. We also sequenced an entire ~50 kbp expansion, which has not been achieved previously for DM2 or any other repeat-expansion disorders. Our approach precisely counted the repeats and identified the repeat pattern for both short interrupted and uninterrupted alleles. Interestingly, in the expanded alleles, only two DM2 samples featured the expected pure CCTG repeat pattern, while the other seven presented also TCTG blocks at the 3′ end, which have not been reported before in DM2 patients, but confirmed hereby with orthogonal methods. The demonstrated approach simultaneously determines repeat length, structure/motif, and the extent of somatic mosaicism, promising to improve the molecular diagnosis of DM2 and achieve more accurate genotype–phenotype correlations for the better stratification of DM2 patients in clinical trials.
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Affiliation(s)
| | - Luca De Antoni
- Department of Biotechnology, University of Verona, Verona, Italy
| | - Federica Centofanti
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, Rome, Italy
| | | | - Simone Maestri
- Department of Biotechnology, University of Verona, Verona, Italy
| | | | - Roberto Massa
- Department of Systems Medicine (Neurology), University of Rome Tor Vergata, Rome, Italy
| | | | - Giuseppe Novelli
- Laboratory of Medical Genetics, University of Rome Tor Vergata, Rome, Italy
| | | | - Annalisa Botta
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, Rome, Italy
| | - Marzia Rossato
- Department of Biotechnology, University of Verona, Verona, Italy
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Mangin A, de Pontual L, Tsai YC, Monteil L, Nizon M, Boisseau P, Mercier S, Ziegle J, Harting J, Heiner C, Gourdon G, Tomé S. Robust Detection of Somatic Mosaicism and Repeat Interruptions by Long-Read Targeted Sequencing in Myotonic Dystrophy Type 1. Int J Mol Sci 2021; 22:2616. [PMID: 33807660 PMCID: PMC7962047 DOI: 10.3390/ijms22052616] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 02/26/2021] [Accepted: 02/27/2021] [Indexed: 02/07/2023] Open
Abstract
Myotonic dystrophy type 1 (DM1) is the most complex and variable trinucleotide repeat disorder caused by an unstable CTG repeat expansion, reaching up to 4000 CTG in the most severe cases. The genetic and clinical variability of DM1 depend on the sex and age of the transmitting parent, but also on the CTG repeat number, presence of repeat interruptions and/or on the degree of somatic instability. Currently, it is difficult to simultaneously and accurately determine these contributing factors in DM1 patients due to the limitations of gold standard methods used in molecular diagnostics and research laboratories. Our study showed the efficiency of the latest PacBio long-read sequencing technology to sequence large CTG trinucleotides, detect multiple and single repeat interruptions and estimate the levels of somatic mosaicism in DM1 patients carrying complex CTG repeat expansions inaccessible to most methods. Using this innovative approach, we revealed the existence of de novo CCG interruptions associated with CTG stabilization/contraction across generations in a new DM1 family. We also demonstrated that our method is suitable to sequence the DM1 locus and measure somatic mosaicism in DM1 families carrying more than 1000 pure CTG repeats. Better characterization of expanded alleles in DM1 patients can significantly improve prognosis and genetic counseling, not only in DM1 but also for other tandem DNA repeat disorders.
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Affiliation(s)
- Antoine Mangin
- Centre de Recherche en Myologie, Inserm, Institut de Myologie, Sorbonne Université, F-75013 Paris, France; (A.M.); (L.d.P.); (G.G.)
- Dementia Research Institute, Cardiff University, Cardiff CF10 3AT, UK
| | - Laure de Pontual
- Centre de Recherche en Myologie, Inserm, Institut de Myologie, Sorbonne Université, F-75013 Paris, France; (A.M.); (L.d.P.); (G.G.)
| | - Yu-Chih Tsai
- Pacific Biosciences, Menlo Park, CA 94025, USA; (Y.-C.T.); (J.Z.); (J.H.); (C.H.)
| | - Laetitia Monteil
- Genetics Department of the Hospital of Toulouse, F-31059 Toulouse, France;
| | - Mathilde Nizon
- CHU de Nantes, Service de Génétique Médicale, Laboratoire de Génétique Moléculaire, F-44000 Nantes, France; (M.N.); (P.B.)
| | - Pierre Boisseau
- CHU de Nantes, Service de Génétique Médicale, Laboratoire de Génétique Moléculaire, F-44000 Nantes, France; (M.N.); (P.B.)
| | - Sandra Mercier
- CHU Nantes, Service de Génétique Médicale, Centre de Référence des Maladies Neuromusculaires AOC, F-44000 Nantes, France;
| | - Janet Ziegle
- Pacific Biosciences, Menlo Park, CA 94025, USA; (Y.-C.T.); (J.Z.); (J.H.); (C.H.)
| | - John Harting
- Pacific Biosciences, Menlo Park, CA 94025, USA; (Y.-C.T.); (J.Z.); (J.H.); (C.H.)
| | - Cheryl Heiner
- Pacific Biosciences, Menlo Park, CA 94025, USA; (Y.-C.T.); (J.Z.); (J.H.); (C.H.)
| | - Geneviève Gourdon
- Centre de Recherche en Myologie, Inserm, Institut de Myologie, Sorbonne Université, F-75013 Paris, France; (A.M.); (L.d.P.); (G.G.)
| | - Stéphanie Tomé
- Centre de Recherche en Myologie, Inserm, Institut de Myologie, Sorbonne Université, F-75013 Paris, France; (A.M.); (L.d.P.); (G.G.)
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