AQP4 and Alzheimer disease: The study argued that in these last two groups, the levels of AQP4 concentrations were undetectable in the CSF, with a mean (± standard deviation) of 0.009 ± 0.01 ng/mL for the AD patients, and 0.007 ± 0.007 ng/mL for not-AD patients with dementia, but also for the other clinical conditions examined similar negative results were obtained.