IAPP and type 2 diabetes mellitus: In cynomolgus monkeys with T2DM, Sun et al found increased aggregation and phosphorylation of α-Syn and partial co-localization with IAPP in the pancreatic islets and brain without obvious dopaminergic neuron death in the substantia nigra (SN), which suggests that T2DM may develop prodromal alterations in PD [29].