Plasma neurofilament light chain (NfL) levels significantly correlate with CSF levels (Kuhle et al., 2016), with Weston et al. (2017) finding a marked elevation in plasma NfL in AD patients, which could be comparable to the plasma Aβ1–42:Aβ1–40 ratio in terms of diagnostic efficiency. The gene discussed is NEFL; the disease is Alzheimer disease.