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Published on: May 23, 2013
Frequency and Phenotype of RFC1 Repeat Expansions in Bilateral Vestibulopathy
Andreas Traschütz1, Felix Heindl1, Muhammad Bilal1
1From the Research Division Translational Genomics of Neurodegenerative Diseases (A.T., M. Synofzik), Hertie-Institute for Clinical Brain Research and Center of Neurology, and German Center for Neurodegenerative Diseases (DZNE) (A.T., M. Synofzik), University of Tübingen; Department of Neurology and German Center for Vertigo and Balance Disorders (F.H., A.Z., M. Strupp), University Hospital, Ludwig-Maximilians University, Munich, Germany; Department of Biochemistry (M.B.), Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, Pakistan; Institute of Medical Genetics and Applied Genomics (A.M.H., D.R.), University of Tübingen, Germany; Department of Psychiatry and Psychotherapy (M.B., C.D., O.R., T.H.), Comprehensive Center for Clinical Neurosciences and Mental Health (C3NMH), Medical University of Vienna, Austria; and Center for Rare Diseases (C.D., O.R., T.H.), University of Tübingen, Germany.
Background And Objectives:
Bilateral vestibulopathy (BVP) is a chronic debilitating neurologic disorder with no monogenic cause established so far despite familiar presentations. We hypothesized that replication factor complex subunit 1 (RFC1) repeat expansions might present a recurrent monogenic cause of BVP.
Methods:
The study involved RFC1 screening and in-depth neurologic, vestibulo-oculomotor, and disease evolution phenotyping of 168 consecutive patients with idiopathic at least "probable BVP" from a tertiary referral center for balance disorders, with127 of them meeting current diagnostic criteria of BVP (Bárány Society Classification).
Results:
Biallelic AAGGG repeat expansions in RFC1 were identified in 10/127 patients (8%) with BVP and 1/41 with probable BVP. Heterozygous expansions in 10/127 patients were enriched compared with those in reference populations. RFC1-related BVP manifested at a median age of 60 years (range 34-72 years) and co-occurred predominantly with mild polyneuropathy (10/11). Additional cerebellar involvement (7/11) was subtle and limited to oculomotor signs in early stages, below recognition of classic cerebellar ataxia, neuropathy, and vestibular areflexia syndrome. Clear dysarthria, appendicular ataxia, or cerebellar atrophy developed 6-8 years after onset. Dysarthria, absent patellar reflexes, and downbeat nystagmus best discriminated RFC1-positive BVP from RFC1-negative BVP, but neither sensory symptoms nor fine motor problems. Video head impulse gains of patients with RFC1-positive BVP were lower relative to those of patients with RFC1-negative BVP and decreased until 10 years disease duration, indicating a potential progression and outcome marker for RFC1-disease.
Discussion:
This study identifies RFC1 as the first-and frequent-monogenic cause of BVP. It characterizes RFC1-related BVP as part of the multisystemic evolution of RFC1 spectrum disease, with implications for designing natural history studies and future treatment trials.
Classification Of Evidence:
This study provides Class II evidence that RFC1 repeat expansions cause BVP.
