A number of research groups are building convincing evidence to show that reduced drainage of cerebrospinal fluid is an important contributing factor in the development of neurodegenerative diseases. A sizable fraction of these conditions are characterized by the aggregation of forms of altered or misfolded proteins, such as amyloid-β, tau, and α-synuclein. They precipitate to form solid deposits surrounded by a complex halo of biochemistry that harms and eventually kills brain cells. From what is known of amyloid-β, levels are quite dynamic, which all along has suggested that rising amounts in older brains are the result of a growing imbalance between processes of creation and clearance, rather than a slow accumulation over time.
For amyloid-β this informs a range of thinking about the condition, such as viral theories that see amyloid formation as an innate immune response run wild in patients with persistent infection. Or theories involving dysfunction of filtration of cerebrospinal fluid in the choroid plexus, or age-related dysfunction of microglia and other cells responsible for clearing up unwanted metabolic waste such as protein aggregates. Theories focused on the more mechanical aspects of fluid clearance are more recent, and in many ways easier to work with