The coexistence of type 2 diabetes mellitus (T2DM) with PD results in more rapid motor and cognitive progression.234–237 Faster progression appears to be independent from the existence of vascular disease in the brain238 and at least in part explained by disruptions in physiological brain insulin signalling (central insulin resistance)239 contributing to neurodegeneration.240. Here, INS is linked to type 2 diabetes mellitus.