Seven potential CSF biomarkers in PD, including amyloid precursor protein (APP), α-synuclein (α-syn), Tau, neurofilament, light gene (NF-L), DJ-1/PARK7, Fractalkine and Neurosin, were selected for quantitative RT-PCR experiments using CSF exosomal RNA from 28 AD, 47 PD, and 27 healthy controls. The gene discussed is KLK6; the disease is Alzheimer disease.