The present study evaluates serum neurofilament light chain (NfL) as a biomarker of disease features in Friedreich's ataxia (FRDA). NfL levels from serum of 117 subjects (85 FRDA patients, 13 carriers, and 19 controls) were assayed and correlated with disease features such as smaller GAA repeat length (GAA1), age, sex, and level of neurological dysfunction. Mean serum NfL levels were higher in FRDA patients than in carriers or unaffected controls in two independent cohorts of subjects. In longitudinal samples from FRDA patients drawn monthly or 1 year apart, values changed minimally. No difference was noted between carriers and controls. NfL levels correlated positively with age in controls and carriers of similar age, (Rs = 0.72, p < 0.0005), whereas NfL levels inversely correlated with age in FRDA patients (Rs = - 0.63, p < 0.001). NfL levels were not associated with sex or GAA1 length in patients, and linear regression revealed a significant relationship between NfL levels in the cohort with age (coefficient = - 0.36, p < 0.001), but not sex (p = 0.64) or GAA1 (p = 0.13). Because NfL is elevated in patients, but decreases with age and disease progression, our results suggest that age is the critical determinant of NfL in FRDA (rather than clinical or genetic severity).
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