This evidence includes [255–257] [258, 259]: (i) AD patients often exhibit lower irisin levels in their blood and CSF compared to healthy controls; (ii) irisin levels are inversely associated with AD symptoms, cognitive impairment, brain amyloid deposits, and inflammation; and (iii) specific genetic variations of FNDC5/irisin increase the risk of AD in certain populations. The gene discussed is FNDC5; the disease is Alzheimer disease.