NEFL and X-linked adrenoleukodystrophy: Accordingly, we evaluated: (a) whether NfL levels discriminate early cerebral involvement in X-ALD patients, (b) the value of biomarkers indicative of astrocyte/microglia activation or immune cell recruitment to complement NfL for disease onset and staging, and (c) the prognostic significance of these biomarkers to differentiate CALD-indicative demyelination in an independent phenotype-blinded X-ALD validation cohort.