Current in-vivo molecular biomarkers to aid in diagnosis of sporadic forms of FTLD are limited to nonspecific indicators of neurodegeneration and axonal loss (e.g., neurofilament light chain [NfL]), as well as markers of Alzheimer’s disease (AD) pathology (e.g., Aβ42/40, P-tau181) to rule out AD. Here, NEFL is linked to Alzheimer disease.