NEFL and X-linked adrenoleukodystrophy: Decoding revealed that this NfL cut-off correctly classified 24 out of the 25 boys with X-ALD from the validation cohort according to their MRI-assigned clinical status of cerebral integrity, indicating a prognostic accuracy of 96% [95% CI: 80–100] for blood NfL levels to correctly differentiate CALD in childhood/adolescent X-ALD patients.