HDAC9 and Parkinson disease: The significant role of HAT/HDAC homeostasis is highlighted by an ongoing investigation of a new pharmacological strategy using an HDAC inhibitor (ClinicalTrials.gov number, NCT02046434) for α-synuclein clearance from the brain and a funded study on the modulation of HDAC4 in patients carrying either the LRRK2, GBA, or SNCA mutation as a PD treatment sponsored by Michael J. Fox Foundation.