Additionally, Fang et al.39 evaluated AQP4 polymorphisms in PD together with Positron Emission Tomography measures of beta-amyloid burden, sleep behavior, and CSF biomarkers and observed that AQP4 rs162009 may be a biomarker of cognitive decline in PD, possibly attributable to its role in changing neurofluid circulation. The gene discussed is AQP4; the disease is Parkinson disease.