We wanted to investigate how cognitive integrity (assessed by MoCA) in SUD patients (SUD + CI vs. SUD − CI) could affect plasma concentrations of NfL, BDNF, and the NfL/BDNF ratio using a one-way ANCOVA with “group” (SUD + CI, SUD − CI, dementia and control groups) as a factor and age as a covariate. The gene discussed is NEFL; the disease is dementia.