In this study we analyzed plasma Alzheimer’s disease (AD) core biomarkers, neurofilament light chain (NfL), and glial fibrillary acid protein (GFAP) using the Single Molecule Array (SIMOA) platform in 75 cognitively preserved nonagenarians, and compared with baseline samples of 153 volunteers who were cognitively unimpaired (CU) during six years (classified in ≤ 70, and 71 to 85 years of age), and with 108 AD patients. This evidence concerns the gene NEFL and early-onset autosomal dominant Alzheimer disease.