APOE and Alzheimer disease: The distribution of the ApoE4 variant showed a significant difference among the four groups (p < 0.001), with the ApoE4 allele being more frequent in AD compared to CT, MCI and MD patients (AD vs. CT: p < 0.001; OR: 3.76; 95% CI: 2.43–5.89; AD vs. MCI: p < 0.001; OR: 2.57; 95% CI: 1.54–4.33; AD vs. MD: p < 0.001; OR: 2.20; 95% CI: 1.34–3.64).