The main findings were that plasma NFL (1) correlated with CSF NFL independent of diagnosis, (2) was increased in the AD dementia group and in Aβ-positive patients with MCI, (3) had diagnostic accuracy for AD dementia in the same range as established CSF biomarkers, and (4) was associated with cognitive deficits and neuroimaging hallmarks of AD at baseline and during follow-up. The gene discussed is NEFL; the disease is Alzheimer disease.