Recent studies exploring the role of matrix metalloproteinase-9 (MMP-9)-mediated β-dystroglycan (β-DG) cleavage in the regulation of AQP4 polarity-mediated glymphatic system in PD have revealed reduced perivascular influx and efflux of CSF tracers in an MPTP-induced PD model in mice associated with impaired AQP4 polarization [130]. The gene discussed is AQP4; the disease is Parkinson disease.