Evaluating Cerebrospinal Fluid Biomarkers in Alzheimer's, Progressive Supranuclear Palsy Subjects, and Controls

Primary Objective: To compare the time profile of appearance and disappearance in CSF of pulse deuterium-labeled chromogranin B, sAPPα and β-Trace in AD and PSP subjects compared to healthy controls. Secondary Objectives: * To measure body water enrichment of deuterium in saliva and plasma (2H-enrichment (%)) * To explore the effect of age on the kinetics of deuterium labeling of CSF biomarkers * To assess intra and inter subject variability of deuterium-labeling of chromogranin B, sAPPα and β-Trace Subjects will undergo screening evaluations to determine eligibility prior to heavy water (2H20) administration. Eligible subjects will be admitted to the clinical facility on Day -1. On Day 1, subjects will ingest small doses of 2H20 during their inpatient stay. They will also drink 2H20 for 7 more days. Subjects will undergo two lumbar punctures (LPs) for CSF samples. Subjects will return to the study site approximately 7 days after the last LP (or early termination) for a follow-up assessment and discharge.