APOE and Alzheimer disease: Lastly, we assessed whether specifically the apoE3 and apoE4 isoforms in APOE ε3/ε4 individuals were linked to MMSE scores, CSF AD biomarker levels, Aβ40, and the Aβ42/Aβ40 ratio, as well as CSF α-synuclein and both CSF and plasma levels of KLK6, YKL-40, and NfL.