KLK6 and Alzheimer disease: Using multivariate correlation analyses, we assessed whether plasma apoE levels were related to α-synuclein, KLK6, and YKL-40 and found that in addition to significant associations with cognition (MMSE) and the CSF AD biomarkers (except for Aβ40), low levels of plasma apoE were related to higher CSF KLK6 and α-synuclein levels specifically in aMCI patients converting to ADD.