APOE and Alzheimer disease: PET with N-[11C]methyl-4-piperidyl acetate ([11C]MP4A), another selective AChE radioligand, has shown that AD patients with apolipoprotein E allele ɛ4 (ApoE4) have significantly less pronounced reductions in cortical AChE activity than those negative for the ApoE4 allele [22].