APOE and Alzheimer disease: The levels of CSF Aβ42 were much lower in APOE ε4 positive participants between CN ε4− and CN ε4+ groups (p < 0.001), between MCI ε4− and MCI ε4+ groups (p < 0.001), and between AD ε4− and AD ε4+ groups (p = 0.031).