Whilst studies have shown a relationship between serum and plasma NfL levels and cognition in people with mild cognitive impairment (MCI) (Lewczuk et al., 2018; Mattsson et al., 2019; Osborn et al., 2019) and AD (Lewczuk et al., 2018; Mattsson et al., 2019; Quiroz et al., 2020), the relationship between serum NfL levels and pre-clinical changes in cognitive status in unimpaired adults is less understood. The gene discussed is NEFL; the disease is Alzheimer disease.