MT-RNR2 and Alzheimer disease: Humanin (HN) is a 24 amino acid polypeptide (Met- Ala- Pro- Arg- Gly- Phe- Ser- Cys- Leu- Leu- Leu- Leu- Thr- Ser- Glu- Ile- Asp- Leu- Pro- Val- Lys- Arg- Arg- Ala; M.W. = 2656.3 Da) that was first identified from a cDNA library from the surviving neurons of human Alzheimer's disease (AD) brain [1].