A literature review was performed by searching PubMed for articles published between 2012 and 2024, using the keywords ‘fibronectin type III domain-containing 5 (FNDC5)’, ‘irisin’, ‘cognitive impairment’, ‘Alzheimer’s disease’, ‘Age-related cognitive dysfunction’ and ‘Diabetes-associated cognitive dysfunction’, combined with Boolean operators (AND/OR). The gene discussed is FNDC5; the disease is diabetes mellitus.