Therefore, this review aims to build upon current neuroendocrinological and psychopathological research by integrating the roles and interrelationships of five key mechanisms— E2, ALLO, GABAergic system, 5-HT transmission, and the APOE genotype—in the context of both PMDD and AD, thereby attempting to construct a theoretical framework linking the two disorders. The gene discussed is APOE; the disease is Alzheimer disease.