The European Friedreich’s Ataxia Consortium for Translational Studies (EFACTS) is a prospective international registry investigating the natural history of Friedreich’s ataxia. We used data from EFACTS to assess disease progression and the predictive value of disease-related factors on progression, and estimated sample sizes for interventional randomised clinical trials.
We enrolled patients with genetically confirmed Friedreich’s ataxia from 11 European study sites in Austria, Belgium, France, Germany, Italy, Spain, and the UK. Patients were seen at three visits—baseline, 1 year, and 2 years. Our primary endpoint was the Scale for the Assessment and Rating of Ataxia (SARA). Secondary outcomes were the Inventory of Non-Ataxia Signs (INAS), the Spinocerebellar Ataxia Functional Index (SCAFI), phonemic verbal fluency (PVF), and the quality of life measures activities of daily living (ADL) and EQ-5D-3L index. We estimated the yearly progression for each outcome with linear mixed-effect modelling. This study is registered with ClinicalTrials.gov, number NCT02069509, and follow-up assessments and recruitment of new patients are ongoing.
Between Sept 15, 2010, and Nov 21, 2013, we enrolled 605 patients with Friedreich’s ataxia. 546 patients (90%) contributed data with at least one follow-up visit. The progression rate on SARA was 0·77 points per year (SE 0·06) in the overall cohort. Deterioration in SARA was associated with younger age of onset (–0·02 points per year [0·01] per year of age) and lower SARA baseline scores (–0·07 points per year [0·01] per baseline point). Patients with more than 353 GAA repeats on the shorter allele of the FXN locus had a higher SARA progression rate (0·09 points per year [0·02] per additional 100 repeats) than did patients with fewer than 353 repeats. Annual worsening was 0·10 points per year (0·03) for INAS, −0·04 points per year (0·01) for SCAFI, 0·93 points per year (0·06) for ADL, and −0·02 points per year (0·004) for EQ-5D-3L. PVF performance improved by 0·99 words per year (0·14). To detect a 50% reduction in SARA progression at 80% power, 548 patients would be needed in a 1 year clinical trial and 184 would be needed for a 2 year trial.
Our results show that SARA is a suitable clinical rating scale to detect deterioration of ataxia symptoms over time; ADL is an appropriate measure to monitor changes in daily self-care activities; and younger age at disease onset is a major predictor for faster disease progression. The results of the EFACTS longitudinal analysis provide suitable outcome measures and sample size calculations for the design of upcoming clinical trials of Friedreich’s ataxia.