• Andreas Traschütz, Andrea Cortese, Selina Reich, Natalia Dominik, Jennifer Faber, Heike Jacobi, Annette M Hartmann, Dan Rujescu, Solveig Montaut, Andoni Echaniz-Laguna, Sevda Erer, Valerie Cornelia Schütz, Alexander A Tarnutzer, Marc Sturm, Tobias B Haack, Nadège Vaucamps-Diedhiou, Helene Puccio, Ludger Schöls, Thomas Klockgether, Bart P van de Warrenburg, Martin Paucar, Dagmar Timmann, Ralf-Dieter Hilgers, Jose Gazulla, Michael Strupp, German Moris, Alessandro Filla, Henry Houlden, Mathieu Anheim, Jon Infante, A Nazli Basak, Matthis Synofzik, and RFC1 Study Group.
• From the Department of Neurodegenerative Diseases (A.T., S.R., L.S., M. Synofzik), Hertie-Institute for Clinical Brain Research and Center of Neurology, and German Center for Neurodegenerative Diseases (DZNE) (A.T., S.R., L.S., M. Synofzik), University of Tübingen, Germany; MRC Centre for Neuromuscular Diseases (A.C., N.D., H.H.), Department of Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, UCL Queen Square Institute of Neurology, London, UK; Department of Brain and Behaviour Sciences (A.C.), University Pavia, Italy; Department of Neurology (J.F., T.K.), University Hospital Bonn; German Center for Neurodegenerative Diseases (DZNE) (J.F., H.J., T.K.), Bonn; Department of Neurology (H.J.), University Hospital of Heidelberg; Department of Psychiatry, Psychotherapy and Psychosomatics (A.M.H., D.R.), University of Halle, Germany; Département de Neurologie (S.M., M.A.), Hôpital de Hautepierre, Hôpitaux Universitaires de Strasbourg; Department of Neurology (A.E.-L.), APHP, CHU de Bicêtre; French National Reference Center for Rare Neuropathies (NNERF) (A.E.-L.); Inserm U1195 and Paris-Sud University (A.E.-L.), Le Kremlin Bicêtre, France; Medical Faculty (S.E.), Department of Neurology, Uludag University, Bursa, Turkey; University of Zurich (V.C.S., A.A.T.); Department of Neurology (V.C.S., A.A.T.), University Hospital Zurich, Switzerland; Institute of Medical Genetics and Applied Genomics (M. Sturm, T.B.H.) and Center for Rare Diseases (T.B.H.), University of Tübingen, Germany; Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC) (N.V.-D., H.P.); INSERM (N.V.-D., H.P.), U1258; CNRS (N.V.-D., H.P.), UMR7104, Illkirch; Université de Strasbourg (H.P.), France; Department of Neurology (B.P.v.d.W.), Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, the Netherlands; Department of Neurology (M.P.), Karolinska University Hospital; Department of Clinical Neuroscience (M.P.), Karolinska Institute, Stockholm, Sweden; Department of Neurology (D.T.), Essen University Hospital, University of Duisburg-Essen, Essen; Department of Medical Statistics (R.-D.H.), RWTH Aachen University, Germany; Department of Neurology (J.G.), Hospital Universitario Miguel Servet. Zaragoza, Spain; Department of Neurology (M. Strupp), University Hospital, and German Center for Vertigo and Balance Disorders (M.Strupp), Ludwig Maximilians University, Munich, Germany; Neurology Service (G.M.), Hospital Unversitario Central de Asturias (HUCA), SESPA, Oviedo, Spain; Department of Neurosciences and Reproductive and Odontostomatological Sciences (A.F.), Federico II University Naples, Italy; Institute of Genetics and Molecular and Cellular Biology (M.A.), INSERM-U964/CNRS-UMR7104, University of Strasbourg, Illkirch; Strasbourg Federation of Translational Medicine (M.A.), University of Strasbourg, Strasbourg, France; Service of Neurology (J.I.), University Hospital "Marqués de Valdecilla (IDIVAL)," University of Cantabria, "Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED)," Santander, Spain; and Suna and Inan Kıraç Foundation (A.N.B.), Neurodegeneration Research Laboratory, KUTTAM, Koç University School of Medicine, Istanbul, Turkey.
• Neurology. 2021 Mar 2; 96 (9): e1369-e1382.

ObjectiveTo delineate the full phenotypic spectrum, discriminative features, piloting longitudinal progression data, and sample size calculations of replication factor complex subunit 1 (RFC1) repeat expansions, recently identified as causing cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS).MethodsMultimodal RFC1 repeat screening (PCR, Southern blot, whole-exome/genome sequencing-based approaches) combined with cross-sectional and longitudinal deep phenotyping in (1) cross-European cohort A (70 families) with ≥2 features of CANVAS or ataxia with chronic cough (ACC) and (2) Turkish cohort B (105 families) with unselected late-onset ataxia.ResultsPrevalence of RFC1 disease was 67% in cohort A, 14% in unselected cohort B, 68% in clinical CANVAS, and 100% in ACC. RFC1 disease was also identified in Western and Eastern Asian individuals and even by whole-exome sequencing. Visual compensation, sensory symptoms, and cough were strong positive discriminative predictors (>90%) against RFC1-negative patients. The phenotype across 70 RFC1-positive patients was mostly multisystemic (69%), including dysautonomia (62%) and bradykinesia (28%) (overlap with cerebellar-type multiple system atrophy [MSA-C]), postural instability (49%), slow vertical saccades (17%), and chorea or dystonia (11%). Ataxia progression was ≈1.3 Scale for the Assessment and Rating of Ataxia points per year (32 cross-sectional, 17 longitudinal assessments, follow-up ≤9 years [mean 3.1 years]) but also included early falls, variable nonlinear phases of MSA-C-like progression (SARA points 2.5-5.5 per year), and premature death. Treatment trials require 330 (1-year trial) and 132 (2-year trial) patients in total to detect 50% reduced progression.ConclusionsRFC1 disease is frequent and occurs across continents, with CANVAS and ACC as highly diagnostic phenotypes yet as variable, overlapping clusters along a continuous multisystemic disease spectrum, including MSA-C-overlap. Our natural history data help to inform future RFC1 treatment trials.Classification Of EvidenceThis study provides Class II evidence that RFC1 repeat expansions are associated with CANVAS and ACC.Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.

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