Limitations of the autopsy data include the limited percentage of brain samples from PD patients with cognitive impairment, single-hemisphere analyses in diseases that have asymmetric motor features, the limited number of autopsy brain samples available which precluded correction for age and sex, and the potential for uncontrolled factors such as mechanism of death and/or postmortem interval to impact measurement of HDAC expression in brain tissue. Here, HDAC9 is linked to Parkinson disease.