GHRL and Parkinson disease: Decreased levels of some bacterial families (such as Prevotellaceae, Lactobacillaceae, Lachnospiraceae) in PD patients are interesting in terms of their ability to reduce short-chain fatty acid (SCFA) levels (Scher et al., 2013; Zmora et al., 2019) or ghrelin (Song et al., 2017; Yanagi et al., 2017).