HDAC9 and obesity due to melanocortin 4 receptor deficiency: Intestinal butyric acid plays a significant role in the prevention and management of obesity and insulin resistance through the activation of G-protein-coupled receptors (GPCRs) (Kim et al., 2013; Kim et al., 2014; D'Souza et al., 2017; Wang et al., 2024) and the inhibition of histone deacetylase (HDAC) (Davie, 2003; Steliou et al., 2012; Chriett et al., 2017; Wang et al., 2024).