FNDC5 and early-onset autosomal dominant Alzheimer disease: In addition, patients with Alzheimer’s disease and mice with neurodegenerative disease were reported to have reduced FNDC5 and irisin levels in their cerebrospinal fluid (CSF) and hippocampus, and in these patients and mice, FNDC5 and irisin expression restoration was noted to improve synaptic plasticity and memory [28].