PSEN1 and Alzheimer disease: The most common occurring genetic risk locifor the EOAD include chromosomes 21, 14, and 1, which harbor amyloid-β(Aβ) precursor protein (APP), presenilin 1 (PSEN1), and presenilin2 (PSEN2), respectively. Consequently,adult patients with Down syndrome (trisomy 21) who survive beyondthe age of 45 years tend to develop neurocognitive decline and clinicopathologicalfeatures of AD.−,