MUC5AC and Parkinson disease: Apart from SCFA-producing bacteria being altered, mucin-degrading bacteria including Akkermansia muciniphila could also be involved in PD pathology with genetic variations in mice showing the expression of this bacteria to be increased (Guardia-Escote et al., 2020), and the same genetic variation, apolipoprotein E4, also related to an increased incidence of PD in humans (Singh et al., 2014).