Abstract
Apolipoprotein E (APOE) remains the most robust and widely replicated genetic risk factor for late-onset Alzheimer's disease (AD) susceptibility, with the ε4 allele (APOE4) demonstrating profound associations with accelerated symptom manifestation, enhanced disease trajectory, and modified therapeutic responsiveness. This comprehensive review synthesizes contemporary evidence regarding the clinical utility of APOE4 genotyping, emphasizing its integration into personalized therapeutic frameworks and early diagnostic paradigms. The APOE4 variant exerts pathogenic influence through impaired amyloid-β clearance, enhanced tau pathology, and compromised neuronal repair mechanisms that alter disease phenotype. We systematically examine available genotyping methodologies, encompassing polymerase chain reaction (PCR) and next-generation sequencing (NGS) platforms, and evaluate their practical implementation within clinical environments. Recent investigations demonstrate that APOE4 status profoundly influences therapeutic efficacy, particularly with anti-amyloid interventions such as lecanemab, where carriers exhibit enhanced treatment response alongside increased adverse event susceptibility. Emerging gene therapeutic approaches show promise in mitigating APOE4-associated risks through targeted molecular interventions. The integration of APOE4 genotyping with fluid biomarkers and neuroimaging techniques enables refined patient stratification and enhanced diagnostic precision, facilitating earlier intervention windows that optimize therapeutic outcomes before irreversible neuronal damage occurs. This review underscores APOE4 testing as a transformative component of precision medicine in AD management, emphasizing its contribution to diagnostic refinement, clinical decision support, and targeted therapeutic interventions.