Taking these findings into disease context, reduced irisin levels were found in the hippocampus and cerebrospinal fluid (CSF) of AD patients and in hippocampi of experimental AD models.126 Knockdown of brain irisin in mice impaired synaptic plasticity and memory function, both of which were rescued by boosting central or peripheral irisin levels. The gene discussed is FNDC5; the disease is Alzheimer disease.