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). The gene discussed is HDAC9; the disease is cardiac arrhythmia.