TH and autism spectrum disorder: Shah et al. reported that butyric acid can regulate tyrosine hydroxylase (TH) mRNA levels in a PC12 cell model (Shah et al., 2006), and Nankova et al. reported that SCFAs such as propionic acid and butyric acid produced by gastrointestinal bacteria are involved in the development of neuronal disorders including autism spectrum disorders influencing brain monoaminergic pathways (gut–brain axis) (Nankova et al., 2014).