PSEN2 and familial Alzheimer disease: Humanin was discovered in 2001 as a 24-mer peptide that inhibited neuronal cell death induced by neurotoxic amyloid-β (Aβ) peptides and by mutants of familial Alzheimer’s disease (FAD) genes, i.e., APP amyloid precursor protein (APP), presenilin-1 (PS1), and presenilin-2 (PS2) [1,2,3].