In cognitively normal PD, our finding of elevated HDAC density in the precentral gyrus fits well with previous observations in PD animal models showing beneficial effects of class I HDAC inhibitors.(11, 14, 16, 18–20, 23) Together, these observations suggest that clinical trials in cognitively normal PD targeting motor function with a class I HDAC inhibitor may have therapeutic potential. This evidence concerns the gene HDAC9 and Parkinson disease.