GRN and frontotemporal dementia: Serum NfL is inversely correlated with survival time.66 Furthermore, presymptomatic cases have shown elevated NfL within serum before disease manifestation.67 Consistent with this, serum NfL was one of the earliest identified altered markers in frontotemporal dementia GRN-mutation carriers.68 Plasma NfL also has prognostic value with plasma NfL elevation occurring in asymptomatic frontotemporal dementia mutation carriers preceding disease onset.69