Plasma p-tau levels have not been as successful in predicting outcomes in PD, although they correlate well with CSF p-tau levels and are established in Alzheimer’s as a biomarker of tau and beta-amyloid pathology: levels of phosphorylated tau at threonine 181 (p-tau181) are not increased in PD patients who progress to dementia141,183. This evidence concerns the gene MAPT and Parkinson disease.