Our serum NfL concentrations for symptomatic FAD are similar to a recent study of sporadic AD that used the same ultrasensitive immunoassay approach.22 The mean concentration for our symptomatic group (46.0 pg/mL) (which contained a mixture of mild cognitive impairment [MCI] and AD dementia) lies between their mean values for separate sporadic MCI (42.8 pg/mL) and AD dementia (51.0 pg/mL) groups. Here, NEFL is linked to Cognitive impairment.