FNDC5 and Alzheimer disease: Lourenco et al. (2019) elucidated that FNDC5/irisin was decreased in AD brains and CSF and in AD experimental models, but there was no significance in plasma irisin levels. Conti et al. (2019) reported a slight increase in irisin serum levels in patients with AD. Zhang et al. (2021) suggested that serum irisin might be a biomarker of cognitive decline in vascular dementia. Bičíková et al. (2021) reported that movement was a positive modulator of aging and the PPARγ is a critical link between mental function and aging.