We assessed the total plasma and apoE isoform levels in baseline samples from a longitudinally (24 months) followed cohort of patients with amnestic mild cognitive impairment (aMCI) or ADD, versus controls, and investigated potential associations with disease progression, cognition, AD pathology as assessed using the Amyloid, Tau and Neurodegeneration (A/T/N) classification, and CSF AD biomarkers, α-synuclein, neurofilament light chain (NfL), YKL-40 and kallikrein 6 (KLK6) levels in CSF or plasma. The gene discussed is KLK6; the disease is Alzheimer disease.