AQP4 and diabetes mellitus: Our data showed the trend of a reduction in the AQP4 expression with an increased severity of DM, and a clinical investigation of idiopathic normal pressure hydrocephalus (iNPH) patients also found an attenuated expression of peri-vascular AQP4 in iNPH, potentially contributing to slow waste clearance, impaired glymphatic circulation, and subsequent neurodegeneration [59].