It was found that the acetylation level of histone H4 is significantly decreased in the frontal cortex and hippocampus of AD transgenic mice and primary neurons cultured from AD transgenic mice, while the HDAC inhibitor 4-PBA can increase the gene transcription of many genes and reverse the spatial learning and memory impairment of AD mouse models (Ricobaraza et al., 2009). The gene discussed is HDAC9; the disease is Alzheimer disease.