BackgroundHeterozygous GAA expansions in the FGF14 gene have been related to autosomal dominant cerebellar ataxia (SCA27B‐MIM:620174). Whether they represent a common cause of sporadic late‐onset cerebellar ataxia (SLOCA) remains to be established.ObjectivesTo estimate the prevalence, characterize the phenotypic spectrum, identify discriminative features, and model longitudinal progression of SCA27B in a prospective cohort of SLOCA patients.MethodsFGF14 expansions screening combined with longitudinal deep‐phenotyping in a prospective cohort of 118 SLOCA patients (onset >40 years of age, no family history of cerebellar ataxia) without a definite diagnosis.ResultsPrevalence of SCA27B was 12.7% (15/118). Higher age of onset, higher Spinocerebellar Degeneration Functional Score, presence of vertigo, diplopia, nystagmus, orthostatic hypotension absence, and sensorimotor neuropathy were significantly associated with SCA27B. Ataxia progression was ≈0.4 points per year on the Scale for Assessment and Rating of Ataxia.ConclusionsFGF14 expansion is a major cause of SLOCA. Our natural history data will inform future FGF14 clinical trials. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Background and Objectives:Nigro-striatal dopaminergic denervation (NSDD) remains poorly characterized in cerebellar multiple system atrophy (MSA-C). We aimed to study NSDD progression in MSA-C and evaluate the capacity for [123I]-FP-CIT-SPECT and parkinsonism to differentiate MSA-C from idiopathic late-onset cerebellar ataxia (ILOCA).Material and methods:We included 85 patients successively referred for sporadic late-onset cerebellar ataxia (SLOCA). Every six months, SARA, UPDRS-III and SDFS scores were measured, and MSA-C diagnostic criteria were searched for. Striatal/occipital dopaminergic binding ratio was evaluated every year with [123I]-FP-CIT-scintigraphy.Results:After a mean follow-up of 33.8 months, 33 patients had probable MSA-C, 8 possible MSA-C and 44 ILOCA. SARA and UPDRS-III scores worsened faster in the probable MSA-C group (p<0.01) compared to the ILOCA group. Baseline striatal/occipital ratio was lower (2.3 vs 2.97; p<0.01) and more decreasing among probable MSA-C patients (p<0.01). Weighting dysautonomia and parkinsonism and/or NSDD as additional and principal criterion, respectively, in the possible MSA-C diagnostic criteria slightly improved their specificity (81.6% vs 76.9%) and sensitivity (77.8% vs 72.2%) to predict a final diagnosis of probable MSA-C.Conclusions:Rapid symptoms worsening and NSDD existence and progression predict MSA-C among SLOCA patients. Parkinsonism, NSDD and dysautonomia should be considered equivalent for possible MSA-C diagnosis.