Recent studies in adolescents with mitochondrial disease have identified a direct correlation between Nf-L levels in CSF and the severity of brain degeneration.5 This biomarker can also be found in the CSF of patients affected by other conditions, such as multiple sclerosis6 and Alzheimer’s disease7; the high concentrations of Nf-L correlate with the progression6 and severity7 of these conditions, confirming the prognostic value of Nf-L as a marker of neuroinflammation. Here, NEFL is linked to mitochondrial disease.