HDAC9 and early-onset autosomal dominant Alzheimer disease: Lastly, alterations in HAT and HDAC levels and activity have been described in several neurodegenerative diseases, such as HD [43, 60, 61], Alzheimer’s disease (AD) [62, 63], Parkinson’s disease (PD) [64, 65], amyotrophic lateral sclerosis (ALS) [66, 67], and spinal muscle atrophy (SMA) [68].