IAPP and early-onset autosomal dominant Alzheimer disease: It is well known that the toxic amyloid-like aggregates of β-amyloid (APP), tau (MAPT), α-synuclein (SNCA or PARK1), and islet amyloid polypeptide (IAPP) are linked with neurodegeneration in Alzheimer’s disease (AD), frontotemporal dementia (FTD), Parkinson’s disease (PD) or Type 2 diabetes (T2D) [75].