FNDC5 and Alzheimer disease: Tsai et al. explored the circulating level of irisin and neurocognitive performance of thirty-two individuals with a family history of AD (ADFH) and obesity (ADFH-obesity group) and 32 controls (ADFH-non-obesity group) during a visuospatial working memory task and discovered the direct proportion between serum irisin levels and cognitive function in cognitively normal individuals, which indicates the protective role of irisin in the brain (44).