Neurofilament light (NfL), most prevalent and soluble neurofilament subunit in both CSF and blood, is a key biomarker for different neurologic diseases.55 Significantly elevated blood NfL levels were observed at diagnosis in presymptomatic and symptomatic patients with MLD and correlated with MRI abnormalities.55 Rapid disease progression in late-infantile and early-juvenile patients was associated with higher NfL levels. Here, NEFL is linked to metachromatic leukodystrophy.