HDAC9 and cardiac arrhythmia: Additionally, clinical trials of HDAC inhibitors have revealed numerous adverse reactions in patients, including thrombocytopenia-induced bleeding, neutropenia-induced susceptibility to infections, anemia due to hemoglobin reduction, arrhythmias, myocardial hypertrophy, and neurotoxicity, which also pose major limitations in the development of HDAC inhibitors (262).