MUC5AC and Parkinson disease: Furthermore, bacteria of the genus Akkermansia, seen to be increased in the PD microbiome (Keshavarzian et al., 2015; Bedarf et al., 2017; Hill-Burns et al., 2017; Heintz-Buschart et al., 2018; Lin et al., 2018; 2019; Li et al., 2019; Nuzum et al., 2020; Romano et al., 2021) are established to be mucin degraders which can therefore, in addition to the lack of butyrate stimulating mucin production, contribute to an increased intestinal epithelial permeability in PD (Nuzum et al., 2020; Nishiwaki et al., 2022).