IGF1 and Alzheimer disease: The association between type-2 DM and AD is complex, and both are interlinked with similar underlying mechanisms including insulin resistance, insulin growth factor (IGF) signalling, inflammatory response, oxidative stress, glycogen synthase kinase 3β (GSK-3β) signalling mechanism, cholinergic impairment, Aβ aggregation, neurofibrillary tangle formation, among others [18].