A Randomized, Parallel-arm, Double Blind, Placebo-controlled Study to Assess the Efficacy of Fampridine for Patients With Spinocerebellar Ataxia SCA27B Caused by a GAA Expansion in the FGF14 Gene

Inclusion Criteria: * Genetic diagnosis of spinocerebellar ataxia SCA27B caused by an expansion ≥ 250 GAA repeats in the FGF14 gene * At least 18 years of age * SARA total score \> 3 and score ≥ 1 on the "gait" item of the SARA scale. * Physically able and expected to complete the trial as designed and having the ability to take oral medication * Signature of informed consent * Covered by social security Exclusion Criteria: * Hypersensitivity to fampridine * Hypersensitivity to any excipients present in fampridine * Serious systemic illnesses or conditions known for enhancing the side-effects of fampridine (i.e., creatinine clearance \< 50 ml/min, hepatic insufficiency, medically significant heart conduction disorders such as occurrence of torsades de pointes or another severe ventricular arrhythmia, high-degree atrioventricular block (Mobitz II or complete), Brugada pattern, QTcF time of \>480 msec in 3 consecutive ECG recordings taken at least 5 minutes apart, uncompensated cardiovascular disorder, epilepsy) * Unstable, clinically significant neurologic (other than the disease being studied; eg, recurrent strokes), psychiatric, cardiovascular (eg, pulmonary arterial hypertension, cardiac valvulopathy, orthostatic hypotension/tachycardia), pulmonary, hepatic, renal, metabolic, gastrointestinal, urologic, immunologic, hematopoietic, or endocrine disease or other abnormality which may impact the ability of the participant to participate or potentially confound the study results. * Patients with known recurrent, active, or chronic infections. * Patients with prior history of seizure. * Concurrent treatment with other medicinal products containing fampridine (4-aminopyridine). * Concomitant use of Fampyra with medicinal products that are inhibitors or substrates of Organic Cation Transporter 2 (OCT2) for example, cimetidine. * Participation in another clinical trial with an investigational drug or receipt of an investigational product within 12 weeks or 5 times the half-life of the product (whichever is longer) prior to Baseline visit * Previous treatment with fampridine * Patients considered at risk of suicidal behavior based on the Columbia-Suicide Severity Rating Scale (C-SSRS), defined as reporting suicidal ideation with intent to act (C-SSRS items 4 or 5) within the 6 months prior to randomization, or any suicidal behavior (including actual, aborted, or interrupted attempts) within the past 12 months. * Pregnancy and breastfeeding (women in childbearing potential will have a urine pregnancy test at each visit) * Sexual non abstinence or absence of effective contraception (for child-bearing aged women, contraception using highly effective methods (see section 6.2 of the protocol) for the duration of treatment and up to 7 days after the last dose of treatment) * Inability to understand information about the protocol * Legally incapacitated adults (e.g., individuals under legal protection such as guardianship or curatorship) * Persons deprived of their liberty by judicial decision * Other ataxic syndromes than SCA27B