Researchers studying a rare genetic condition tied to high psychosis risk have found that the brain’s waste-clearing plumbing, known as the glymphatic system, may function abnormally in people who develop hallucinations. The study, which tracked brain changes over time in individuals with 22q11.2 deletion syndrome, offers one of the first direct links between impaired glymphatic drainage and the kind of neural instability that produces psychotic symptoms. The findings add biological specificity to a growing body of evidence that the brain’s failure to flush out metabolic debris could be a shared driver behind psychiatric disorders ranging from schizophrenia to Parkinson’s disease.
A Genetic Window Into Psychosis Risk
22q11.2 deletion syndrome is a chromosomal condition that roughly triples the odds of developing schizophrenia. That elevated risk makes it a valuable natural experiment for researchers trying to identify what goes wrong in the brain before full psychosis sets in. In a recent longitudinal imaging study in individuals with this deletion, investigators used diffusion MRI to estimate glymphatic-related function through a metric called the DTI-ALPS index, reporting reduced values in carriers compared with healthy peers and altered developmental trajectories that tracked with hallucination vulnerability, according to data in a psychiatry journal.
The ALPS index has become a standard proxy for glymphatic performance in human imaging research. It measures water diffusion along perivascular spaces, the channels through which cerebrospinal fluid enters brain tissue and carries away waste. A lower score signals sluggish clearance. Separate work in cerebral small vessel disease has used the same metric within a mediation analysis to show how reduced glymphatic function statistically bridges the link between vascular brain lesions and cognitive decline, helping to establish ALPS as a clinically meaningful marker across multiple neurological populations.
In 22q11.2 deletion syndrome, that same proxy now appears to capture a developmental vulnerability. Participants who later reported hallucinations tended to show more pronounced deviations in ALPS trajectories during adolescence, a period when synaptic pruning and excitation–inhibition balance are already in flux. Those patterns align with broader theories that psychosis emerges when networks responsible for filtering sensory information become unstable, allowing internally generated signals to be misinterpreted as external events.
How the Brain’s Drainage Network Breaks Down
The glymphatic system is a sleep-enhanced, astrocyte-driven paravascular network that admits cerebrospinal fluid into brain tissue, where it mixes with interstitial fluid to sweep out proteins and inflammatory byproducts. When this network is compromised, neurotoxic proteins such as beta-amyloid and tau, along with inflammatory mediators, can accumulate in the brain, as summarized by a recent psychiatry review. That toxic buildup does not just threaten neurodegenerative diseases like Alzheimer’s. It may also destabilize the neural circuits responsible for perception, creating conditions where the brain generates sensory experiences with no external source.
This perspective matters because most psychiatric research has historically focused on neurotransmitter imbalances, particularly dopamine, as the primary explanation for hallucinations. The glymphatic hypothesis introduces a different mechanism: structural waste accumulation that disrupts signaling across brain regions. If confirmed in larger trials, it could shift treatment strategies from purely chemical interventions toward approaches that restore the brain’s physical drainage capacity, for example by targeting sleep quality, vascular health, or astrocyte function.
Mechanistically, glymphatic flow is thought to depend on arterial pulsations, aquaporin-4 water channels on astrocytic endfeet, and the integrity of perivascular spaces. Any disruption along that chain (hypertension that stiffens arteries, inflammation that alters astrocytes, or genetic variants that affect aquaporin expression) could in principle slow clearance. Over years, even modest impairments might allow misfolded proteins and inflammatory debris to accumulate in regions that support reality testing, such as the hippocampus and prefrontal cortex.
Converging Evidence Across Disorders
The 22q11.2 deletion findings do not stand alone. A separate line of research in Parkinson’s disease demonstrated that cerebrospinal fluid dynamics measurable with noninvasive neuroimaging relate to disease severity, with weakened coupling between global brain activity and CSF flow tracking alongside clinical decline. While Parkinson’s and schizophrenia present differently, both conditions involve perceptual disturbances, and both now show evidence of impaired glymphatic-related clearance.
In schizophrenia specifically, investigators have reported a lower ALPS index that correlates with more pronounced cognitive impairments and negative symptoms, according to work described in a neuroimaging cohort. In that study, patients with the most reduced perivascular diffusion also tended to perform worst on tests of attention and working memory, suggesting that inefficient waste removal may be tied not only to hallucinations but also to broader cognitive deficits.
Additional evidence comes from a multi-omics investigation that combined brain imaging with fecal 16S rRNA sequencing in a cohort of schizophrenia patients and healthy controls. That analysis found that glymphatic dysfunction correlated with gut dysbiosis, implying that the waste-clearance problem may extend beyond the skull into systemic biology. A review in Psychoradiology, drawing on these and related studies, highlighted decreased ALPS index, diminished BOLD–CSF coupling, and enlarged choroid plexus as recurring signatures across psychiatric disorders. It also noted shared mechanisms including chronic sleep disruption, immune activation, and altered aquaporin-4–related biology.
These converging lines of evidence raise the possibility that glymphatic impairment is not a disease-specific oddity but a transdiagnostic vulnerability factor. In such a model, genetic risk variants, environmental insults, and lifestyle factors like poor sleep could converge on a common pathway of impaired clearance. The resulting accumulation of neurotoxic species would then interact with more traditional neurotransmitter abnormalities to produce the full clinical picture of psychosis, mood disturbance, or cognitive decline, depending on which circuits are most affected.
Why Current Coverage Overstates Simplicity
Popular accounts of glymphatic research often frame it as a clean causal chain: poor drainage leads to toxic buildup, which leads to hallucinations. That framing skips several unresolved problems. The DTI-ALPS index, while widely used, remains a proxy measure. It infers glymphatic function from water diffusion patterns rather than directly observing fluid flow in real time. A recent genetic analysis in a large population sample mapped loci associated with glymphatic-related traits using imaging-derived phenotypes such as perivascular spaces and ALPS-like indicators, but the authors acknowledged that these remain indirect measures of a system first characterized in rodent brains.
There are also technical caveats. Diffusion metrics are sensitive to scanner settings, motion, and comorbid white matter changes. Small shifts in how regions of interest are drawn can alter ALPS values, complicating cross-study comparisons. Moreover, many psychiatric cohorts are modest in size and clinically heterogeneous, making it difficult to disentangle whether glymphatic changes precede symptoms, arise as a consequence of chronic illness, or partly reflect medication effects.
The gap between animal models and human clinical reality remains wide. Experimental work has shown that glymphatic clearance can be modulated in rodents, and that interventions which enhance flow can reduce protein aggregates and improve behavioral readouts. But translating those manipulations into safe, scalable therapies for people is nontrivial. Human brains are larger, sleep architecture is more complex, and comorbidities like cardiovascular disease are common, all of which may blunt the impact of interventions that look promising in tightly controlled laboratory settings.
Genetic data add another layer of complexity. The same Nature Communications study that linked imaging markers to glymphatic-related loci also found overlap with variants associated with vascular traits and immune function, reinforcing the idea that what appears as a “drainage problem” may actually be a composite of multiple biological processes. A companion analysis that used an independent imaging dataset replicated some of these associations but again underscored their indirect nature, urging caution in interpreting glymphatic markers as standalone causal agents.
Where the Field Goes Next
Despite these caveats, the new findings in 22q11.2 deletion syndrome strengthen the case that impaired brain clearance is entwined with psychosis risk. The genetic homogeneity of that syndrome reduces some of the noise that plagues broader psychiatric samples, allowing researchers to track how a defined vulnerability unfolds over time. Longitudinal designs, in which the same individuals are scanned repeatedly across development, will be crucial for determining whether glymphatic changes reliably precede symptom onset.
Future studies are likely to combine ALPS measurements with complementary markers, such as CSF biomarkers of protein aggregation, high-resolution imaging of perivascular spaces, and detailed sleep recordings. Interventional trials that manipulate sleep duration, cardiovascular fitness, or anti-inflammatory treatments, while monitoring glymphatic proxies and clinical outcomes, could help test whether improving clearance meaningfully alters the course of hallucinations or cognitive decline.
For now, the emerging picture is nuanced. Glymphatic dysfunction is unlikely to replace dopamine dysregulation or synaptic pruning abnormalities as the singular explanation for psychosis. Instead, it offers a physical substrate that may interact with those processes, shaping how genetic and environmental risks are translated into symptoms. As methods for visualizing brain fluid dynamics improve, the field will be better positioned to move beyond simple narratives and toward a more integrated model in which the brain’s plumbing, chemistry, and circuitry are all part of the same story.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
