While HDAC inhibitors have been studied for the treatment of a variety of diseases, pan-HDAC inhibitors and class I-selective HDAC inhibitors are often cytotoxic and cause adverse reactions in patients, including thrombocytopenia, neutropenia, gastrointestinal reactions, neurotoxicity, and cardiac arrhythmias (Bruserud et al., 2007). Here, HDAC9 is linked to neutropenia.