Scientific contributions were retrievedby searching PubMed (www.ncbi.nlm.nih.gov/pubmed/) and Scopus (www.scopus.com) databases usingkeywords such as “phosphodiesterase”, “PDE5”,“sildenafil”, “tadalafil”, natural compounds”,“neurodegeneration”, “Alzheimer’s disease”,and their combinations. This evidence concerns the gene PDE5A and Alzheimer disease.