HDAC9 and obesity due to melanocortin 4 receptor deficiency: Gut-derived butyrate is significantly decreased in obesity, and is an important driver of the alterations in the gut–liver axis that underpin obesity, non-alcoholic fatty liver disease, and wider metabolic dysregulation [79], all of which may be suppressed by fingolimod, suggesting unrecognized gut microbiome, butyrate/HDAC inhibitory-like effects of this drug [80,81].