A Preliminary Study on Rapid Quantitative and Qualitative Detection Methods for Apolipoprotein E4 in Plasma

Objective: The APOE {varepsilon}4 genotype is the known most significant risk factor for sporadic Alzheimer's disease (AD), but the association between the blood levels of its encoded apolipoprotein E4 (ApoE4) and AD is poorly understood. Methods: We developed a chemiluminescent quantitative assay and a colloidal gold lateral chromatography qualitative assay to detect ApoE4 protein in plasma samples and compared the results with conventional genotyping. Results: In 185 samples, the plasma ApoE4 protein levels in non-{varepsilon}4 carriers ({varepsilon}2/{varepsilon}3 and {varepsilon}3/{varepsilon}3) were 0.07 +/- 0.23 and 0.05 +/- 0.17 g /mL, respectively; while the levels in {varepsilon}4 carriers ({varepsilon}2/{varepsilon}4, {varepsilon}3/{varepsilon}4, and {varepsilon}4/{varepsilon}4) were 4.58 +/- 1.96, 4.28 +/- 3.49 and 8.27 +/- 9.04 g/mL, respectively. Using a threshold of 1.1 g /mL, the quantitative method achieved a sensitivity of 100% and a specificity of 99.2%, while the qualitative method showed a concordance rate of 96.2% with genotyping. We also observed that among 133 non-{varepsilon}4 carriers, one had plasma ApoE4 protein levels higher than the threshold, which would require further investigation. Conclusion: Quantitative and qualitative detection of ApoE4 protein provides as rapid and accurate method for identifying APOE {varepsilon}4 genotype carriers, offering valuable insights for Alzheimer's disease risk assessment and early intervention.