HDAC9 and obesity due to melanocortin 4 receptor deficiency: Major findings of this study are (1) adipose tissue HDAC9 expression was increased in an HFD-induced mouse model of obesity and positively correlated with BMI in humans, (2) in female HFD-fed mice, adipocyte-specific HDAC9 gene deletion led to reduced weight gain and adipocyte hypertrophy, and improvements in glucose tolerance and insulin sensitivity, despite similar locomotor activity and food consumption.