IGF1 and early-onset autosomal dominant Alzheimer disease: Abnormalities in the insulin/insulin-like growth factor 1 (IGF-1) system (IIS) signalling pathway were thought to play a role in the physiopathological processes of various neurodegenerative disorders, including Alzheimer’s disease, spinocerebellar ataxias (SCAs) and Huntington disease (HD) through various mechanisms [33, 34, 36].