PSEN2 and Alzheimer disease: Approximately 5–6% of AD cases are classified as early-onset AD (EOAD), occurring before the age of 65, with only 0.6% of these exhibiting the causative, autosomal dominant genetic mutations in the Presenilin (PSEN1 and PSEN2) and Amyloid Precursor Protein (APP) genes [3,4].