We study the effect of single point mutation of hIAPP20–29 constituting a hIAPP fibril on its molecular structure, since rat islet amyloid polypeptide (rIAPP) fibril does not induce any type II diabetes in a rat despite similarity between amino acid sequences of hIAPP20–29 and rIAPP [53]. This evidence concerns the gene IAPP and type 2 diabetes mellitus.