When amylin immunoreactivity was assessed in subjects with a synucleinopathy or with AD, we found increased immunoreactivity of amylin compared to that in controls (p = 0.0085 for synucleinopathies, p = 0.0011 for AD) but lower immunoreactivity than in subjects with a normal neuropathological examination and a history of T2DM (p < 0.0001 for synucleinopathies, p < 0.0001 for AD). This evidence concerns the gene IAPP and type 2 diabetes mellitus.