Increase of Plasma Biomarkers in Friedreich's Ataxia: Potential Insights into Disease Pathology.

Background: Therapeutic interventions in Friedreich's ataxia (FRDA) are progressing into clinical trials, and the need for robust and easily accessible biomarkers has arisen.

Objective: This study aimed to consolidate preliminary findings of changes in the levels of neurofilament light (NfL), glial fibrillary acidic protein (GFAP), Tau, and ubiquitin C-terminal hydrolase L1(UCH-L1) in FRDA comparing two large independent cohorts of patients with healthy controls.

Methods: Plasma samples of patients from two large natural history studies (n = 187) and a similar sized cohort of healthy control subjects (n = 127) were assessed using single-molecule array measurements. Age-adjusted biomarker levels were related to patients' genetic profile, clinical progression, and comorbidities, and compared with controls. Sensitivity and specificity were assessed using receiver operating characteristic analyses.

Results: NfL levels were significantly elevated in patients with FRDA younger than 40 years, showing a distinct age-dependent trajectory: levels declined with age in FRDA but increased in controls. Longitudinal data indicated annual NfL reductions between 8% (children) and 13% (young adults < 35 years). This result is discussed in the context of other neurodegenerative conditions, with FRDA being a rare case where NfL levels decrease over time before the age of 40 years. In contrast, tau was consistently elevated across all age groups in FRDA.

Conclusions: NfL is a sensitive biomarker in early FRDA but decreases with age, converging with control values after 35-40 years. This age-dependent pattern must be considered when interpreting the effect of interventions in clinical trials. Especially in younger (age < 10 years) or presymptomatic patients and control subjects, additional longitudinal sampling is warranted. Elevated tau levels suggest involvement in underlying disease pathophysiology. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.