The findings that Aβ42 reduces IGF-1 expression in the brain and leptin increases the basal levels of this neurotrophic factor and reverses the Aβ-induced decrease in IGF-1 may be of relevance to AD as IGF-1 exhibits neurotrophic, neuromodulatory, neuroendocrine, and metabolic actions in the brain [53]. This evidence concerns the gene IGF1 and Alzheimer disease.