Authored by Robert K. Naviaux, MD, PhD

The Cell Danger Response (CDR) is an evolutionarily conserved survival program that predates multicellular life. It is activated when mitochondria detect threat—including infection, toxins, immune activation, oxidative stress, or metabolic stress—triggering a temporary shift away from efficient energy production toward a defensive metabolic state.

Dr. Naviaux, a Professor of Genetics in Biochemical Genetics and Metabolism at the University of California, San Diego, and Co-Director of the Mitochondrial and Metabolic Disease Center, developed the CDR as a systems-biology framework describing how mitochondrial and purinergic signaling coordinate cellular responses to stress, injury, and repair, with broad implications for neurodevelopment, immunity, and chronic disease.

The Three Hit Signaling Model

This study introduces a 3-hit metabolic signaling model to explain the causes and potential prevention of autism spectrum disorder (ASD). ​ The model describes the cell danger response (CDR) and identifies three necessary factors for ASD development:

1. DNA predisposition: Genetic and epigenetic traits create mitochondrial and metabolic hypersensitivity to environmental changes. ​These are PRIMERS.
2. Early CDR activation: Exposure to environmental triggers (e.g., pollution, maternal fever, autoantibodies) during the critical neurodevelopmental window from the late 1^st trimester to 18-36 months of age. ​These are TRIGGERS.
3. Prolonged CDR activation: Persistent or recurrent exposure to these triggers for 3-6 months leading to altered synaptogenesis during early development. ​These are AMPLIFIERS.

Behavior has a chemical basis, and CDR regulates this chemistry. The CDR is a chemical and bioenergetic response to stress. It is a final common denominator that connects the genetic and environmental causes of ASD. ​ Dysregulated purinergic signaling and hypersensitivity to extracellular ATP (eATP) lead to mitochondrial dysfunction, altered calcium signaling, and impaired neurodevelopment, contributing to ASD’s core symptoms. ​

Conclusion: Autism spectrum disorder (ASD) is not the inevitable outcome of any single gene or environmental exposure. The 3-hit model transcends the gene-vs-environment debate and reframes ASD as a treatable neurometabolic and neuroimmune syndrome. The model predicts that by reducing air and water pollution, adding new methods in prenatal care and screening, personalizing postnatal care to treat co-occurring medical conditions and increase neurometabolic resilience, and by developing new eATP targeted therapies, some of ASD’s most disabling symptoms can be improved or prevented.

“The model suggests that 40% to 50% of ASD cases may be preventable if high-risk children can be identified and treated before symptoms occur, since the second and third hits are modifiable. Strategies target decreasing exposure to CRD-activating pollutants and metabolic stresses, providing prenatal and pediatric care supplemented with interventions increasing nutritional and neurometabolic resilience, and developing novel antipurinergic drugs restoring balance to hypersensitive extracellular adenosine triphosphate signaling networks.”

“Since the second and third hits are modifiable, this model predicts that if the children at greatest risk can be diagnosed and treated before symptoms occur, some of these children may never develop ASD, and if diagnosed after symptoms occur, the core symptoms that are most disabling can be decreased significantly,” Dr. Naviaux stated.

Core Features of CDR Activation

• ATP production decreases (reduced iATP) as mitochondria shift from oxidative phosphorylation to glycolysis.
• Reactive oxygen species (ROS) increase, amplifying antimicrobial defenses.
• Extracellular ATP (eATP) is released through membrane channels as a distress signal.
• eATP is released through specialized membrane channels called pannexins and connexins, which open during redox stress and electrical imbalance.
  eATP activates neighboring cells, immune cells, and even distant tissues through the bloodstream.
• Purinergic receptors (P2X/P2Y) are activated, propagating inflammatory and metabolic responses.
• Immune signaling intensifies, including cytokines and inflammasome activity.
• Developmental resources are diverted away from growth, language, synaptic refinement, and social behavior.
• Metabolism of hundreds of molecules: vitamins, metals, folate, amino acids, xenobiotics—shifts as part of a coordinated stress chemistry (ADME regulation).

In a healthy system, this wartime program resolves after the threat ends.
But when the CDR fails to turn off due to mitochondrial fragility, chronic infection, autoimmunity, maternal immune activation, immune deficiency, or toxic exposures, the body becomes locked in a chronic defensive state.

The result is persistent neuroimmune activation and disrupted neurodevelopment.

Chronic CDR in Autism

Chronic CDR in Autism

Chronic CDR explains a large body of findings in autism, especially in children with:

• Regression
• Immune dysregulation
• Oxidative stress
• Redox imbalance
• Mitochondrial dysfunction (Complex I/III deficits, low ATP, elevated lactate:pyruvate)
• Microglial activation and aberrant synaptic pruning

Low activity of CD39 and CD73, enzymes that degrade extracellular ATP, can prolong purinergic signaling, keeping the system stuck in a defensive loop rather than returning to growth and differentiation.

This model reframes autism not as a fixed genetic disability, but as a potentially reversible neurometabolic syndrome in which unresolved danger signaling interrupts normal developmental programs.

Suramin and Antipurinergic Therapy: Mechanistic Rationale

Suramin, a century-old antipurinergic drug, has emerged as a prototype therapy for modulating chronic CDR. It works by blocking purinergic receptors (P2X, P2Y) and inhibiting ATP release through membrane channels.

How Suramin Interrupts Chronic CDR

1. eATP as a Danger Signal

During CDR, mitochondria act as both the siren (releasing ATP) and the first responders (shifting metabolism).
Persistent eATP keeps purinergic receptors activated, perpetuating:

• inflammation
• microglial surveillance
• metabolic shutdown
• reduced cell-cell communication
• impaired neuroplasticity

2. Suramin “silences the siren.”

By blocking eATP receptor activation and dampening ATP release, suramin signals that the danger has passed. This allows the cell to progress through:

• CDR1 → inflammation
• CDR2 → growth and repair
• CDR3 → differentiation and restoration

This transition restores mitochondrial efficiency, reduces neuroinflammation, and reopens developmental windows.

3. Metabolic Effects

Suramin normalizes purine metabolism, reduces oxidative stress, and improves redox balance—domains frequently impaired in ASD. Early trials showed improvements in:

• speech and language
• social engagement
• sleep
• appetite
• sensory integration
• developmental rate

These gains faded as suramin cleared, confirming that ongoing CDR signaling is not a static brain injury, rather it is the bottleneck preventing normal functioning.

Next-generation antipurinergic therapies are in development, offering greater specificity and improved safety profiles.

Biological Signatures of CDR in Autism

Persistent CDR activation produces measurable abnormalities commonly found in ASD:

Mitochondrial Dysfunction

• Elevated lactate:pyruvate
• Hypersensitivity to eATP
• Carnitine abnormalities
• PDH impairment

Redox Imbalance

• Abnormal GSH:GSSG ratio
• Reduced CoQ10
• High ROS

Purinergic Tone

• Elevated eATP signaling
• Urinary purine metabolites
• P2X7 upregulation
• Low CD39/CD73 activity

Neuroinflammation

• Activated microglia (PET imaging)
• Elevated IL-6, TNF-α, IL-1β
• NLRP3 inflammasome activation

Immune Activation & Autoantibodies

• MAR antibodies 
• ANA
• Cytokine signatures
• Folate receptor autoantibodies (FRAA)

These biomarkers can support subtype stratification, measure therapeutic response, and guide intervention design.

Why This Matters for Our Work

The CDR model helps unify decades of findings across immunology, metabolism, neuroinflammation, and environmental health. It aligns directly with the AIC’s mission to advance a biologically grounded, systems-based model of autism.

This framework supports:

• New biomarkers for identifying subtypes
• New targets for therapy
• New approaches to clinical trials
• A path toward recovery for children stuck in chronic CDR states
• A shift away from outdated behavioral-only models

The CDR is central to our broader perspective:
Autism is not one condition; it is the shared neurobiological and developmental response to diverse environmental triggers and amplifiers. These interact with unique genetic features of each child and deserve precision science, not one-size-fits-all assumptions.

Bottom Line

The CDR is not theoretical: it’s a measurable, reversible metabolic state that explains many of the disabling features of autism. It unifies findings across mitochondrial biology, immune dysfunction, neuroinflammation, detoxification pathways, folate/one-carbon metabolism, and synaptic development.

When the CDR is identified and therapeutically modulated, the most disabling symptoms of ASD become treatable.

Suramin and future antipurinergic agents offer a path to “unlocking” normal development by switching the system from defense back to growth.