Autism spectrum disorder may develop through three necessary metabolic hits that converge on the cell danger response, a framework that could reshape prevention strategies and explain why no single gene or environmental factor alone causes the condition, according to a review.
The cell danger response (CDR) represents a whole-body metabolic and bioenergetic response to stressors, initiated by extracellular adenosine triphosphate release and maintained by changes in mitochondrial structure and function. This evolutionarily conserved system creates three phases corresponding to wound healing: inflammation (CDR 1), proliferation (CDR 2), and differentiation (CDR 3). When the acute CDR becomes chronic, it produces what study author Robert K. Naviaux, MD, PhD, of the University of California, San Diego School of Medicine, termed "adaptive hypersensitivity to environmental change." Cells that survive repeated CDR activation adapt by becoming hypersensitive to progressively smaller amounts of extracellular adenosine triphosphate, establishing a long-lasting metabolic memory of triggering stresses.
The three-hit model consists of an inheritance of genes sensitizing mitochondria and intracellular calcium signaling to environmental change (first hit), early exposure to CDR-activating environmental triggers during critical neurodevelopmental windows from late first trimester through 18 to 36 months (second hit), and persistent or recurrent CDR activation for at least 3 to 6 months during this period (third hit), wrote Dr. Naviaux.
Genetic Convergence on Mitochondrial Function
The review cataloged 15 monogenic disorders associated with autism spectrum disorder (ASD), from Fragile X syndrome (35% co-occurrence, relative risk = 12.7) to Timothy syndrome (80% co-occurrence, relative risk = 29.0). Despite their diverse mechanisms, all converge on mitochondrial dysfunction, dysregulated calcium homeostasis, and extracellular adenosine triphosphate signaling. Importantly, no single-gene disorder was found to cause ASD in 100% of the children carrying the mutation.
"This biological fact is evidence that genetic disorders do not cause ASD directly, ie, there is no gene whose primary function is to produce autism," Dr. Naviaux wrote.
The median relative risk for genetic causes was 12.7, while environmental factors carried relative risks ranging from 1.13 for chlorpyrifos to 7.8 for pathologic maternal autoantibodies. Among environmental triggers, the median relative risk was 1.32.
Environmental Stacking and Threshold Effects
Environmental pollutants—including lead, mercury, particulate matter measuring 2.5 µm or less in diameter , and PCB153—disrupt mitochondrial function and activate CDR components. Dr. Naviaux introduced "CDR stacking" to explain how multiple subclinical exposures combine: five chemicals, each increasing the risk by 20%, can additively raise the relative risk from 1.0 to 2.0 (5 stressors × 0.2 = +1.0).
"Mixtures of many chemicals have a synergistic effect on mitochondrial function and can create abnormalities together even when no single chemical is present at damaging concentrations," Dr. Naviaux stated.
Maternal factors during pregnancy carry notable risks, including type 1 diabetes, preeclampsia, fever, and prenatal stress from natural disasters. Each factor triggers innate immunity and inflammatory pathways while disrupting mitochondrial oxidative phosphorylation.
Purinergic Signaling Dysregulation
Central to the model is hypersensitivity to extracellular adenosine triphosphate–related purinergic signaling. When chronically elevated, extracellular adenosine drives intracellular adenosine accumulation through equilibrative nucleoside transporters. This intracellular adenosine inhibits S-adenosylhomocysteine hydrolase, increasing S-adenosylhomocysteine and functioning as a reversible "off switch" for methylation reactions needed for neurotransmitter metabolism, DNA and histone methylation, and glutathione synthesis.
"[S-adenosylhomocysteine hydrolase] is a potent inhibitor of S-adenosylmethionine–-dependent methylation reactions needed for neurotransmitter metabolism, and for DNA and histone methylation, glycine methylation for betaine synthesis, guanidinoacetic acid methylation for creatine synthesis, and phosphatidylethanolamine methylation for membrane phosphatidylcholine lipid synthesis," Dr. Naviaux explained.
Recent untargeted multi-omics studies demonstrated that regardless of original genetic defects or environmental exposures, children with ASD share abnormalities in purine metabolism and purinergic signaling, with dysregulation of canonical purinergic receptors P2X7, P2Y2, P2Y6, and noncanonical P2Y10 receptors.
Failed Excitatory-Inhibitory Transition
When the three-hit criteria are met, normal developmental reversal of excitatory to inhibitory signaling by gamma-aminobutyric acid and purine metabolic networks fails. Metabolomic analysis of newborn dried blood spots showed that despite genetic predisposition and intrauterine CDR activation, additional postnatal factors are required during the critical window from birth to 18 to 36 months. This leads to multimodal sensory and chemical over-responsivity extending beyond the five senses to include heightened neuroception of safety and danger signals.
Cerebellar abnormalities trace to this period. Postnatal dropout of mitochondria-rich Purkinje cells occurs during the neurocritical window in both mouse models and humans, while development of inhibitory gamma-aminobutyric acid-ergic interneurons in the basal ganglia becomes impaired.
Presymptomatic Screening Methods
Multiple presymptomatic screening methods are emerging. Maternal blood metabolomic analysis during the second and third trimester can distinguish high-risk pregnancies from background risk with 90% accuracy, showing hypometabolic changes in mitochondrial amino acid and fatty acid metabolism, glutathione, one-carbon metabolism, proline, polyamine, and microbiome pathways.
Postnatal methods include adenosine triphosphate-stimulated calcium assays in fibroblasts (diagnostic accuracy = 0.83), which reveal notably decreased mean open time of inositol trisphosphate–gated calcium channels (15 milliseconds vs 32 milliseconds in controls). Specialized infant hair metal recurrence quantification analysis identified 81% of children who developed ASD by 4 years when samples were collected in the first month of life.
Newborn dried blood spot analysis enables detection of elevated cytokines (interleukin (IL)-6, IL-8, IL-4, IL-1 beta) and folate receptor alpha autoantibodies. Approximately 18% of children with ASD have two or more of 10 maternal autism-related autoantibodies, conferring 7.8 times the odds.
Phenylketonuria Paradigm
Dr. Naviaux drew parallels to phenylketonuria to demonstrate that even genetic disorders following the three-hit paradigm remain treatable when the metabolic basis is addressed early. Despite the strong monogenic predisposition (phenylalanine hydroxylase gene mutations), phenylketonuria requires exposure to phenylalanine (ubiquitous environmental chemical, second hit) and persistence of toxic phenylketone accumulation for months (third hit) to produce intellectual disability.
"Adults with untreated [phenylketonuria] have an average IQ of 35," the Dr. Naviaux noted. "When treated early, adults with [phenylketonuria] have a near-normal IQ of 91, and lead normal or near-normal lives that are indistinguishable in education, occupation, and quality of life from neurotypical controls," he added.
Among children with phenylketonuria, 50% develop ASD if partially untreated (relative risk = 18.1).
Mitochondrial Dysfunction Patterns
Between 15% and 96% of children with ASD show biomarkers or symptoms of secondary mitochondrial dysfunction. Unlike primary mitochondrial diseases with high childhood mortality, ASD-associated mitochondrial changes represent adaptive responses to chronic extracellular adenosine triphosphate hypersensitivity.
"Under the new paradigm, the apparent mitochondrial dysfunction in ASD and other disorders is not dysfunction at all—the mitochondria are doing exactly as they are instructed," Dr. Naviaux wrote. "The resulting chronic mitochondrial and cellular adaptations are caused by hypersensitivity to eATP signaling," he noted.
Lymphoblastoid cells show increased maximal oxygen consumption and respiratory reserve capacity but undergo brittle collapse when exposed to reactive oxygen species, particularly prominent in children with developmental regression.
Regression and Redox Fragility
Neurodevelopmental regression occurs in 30% of children later diagnosed with ASD when considering language skills alone, and 40% when including social skills. More than 80% of regression events occur between 15 to 30 months, with a mean age of 20 months across 20 studies. This window corresponds to increased synaptic pruning and represents a second period of vulnerability.
In a randomized controlled trial, a 33-nutrient mitochondrial cofactor supplement produced improvements in ASD-associated communication and behaviors, while increasing mitochondrial respiration and reserve capacity.
Co-occurring Medical Conditions
Between 75% and 95% of children with ASD have at least one co-occurring medical condition, leading to the diagnostic entity "autism with co-occurring medical conditions." Common comorbidities include epilepsy, gastrointestinal problems, sleep disorders, asthma, folate receptor–blocking autoantibodies, cerebral folate deficiency, mast cell activation, and immune dysfunction.
"Treatment of the co-occurring medical conditions relieves this competition and returns crucial energy and resources back to the child for optimum development," Dr. Naviaux explained.
A three-stage treatment framework emerges: antipurinergic therapy to desensitize purinergic signaling abnormalities and restore neuroplasticity, treatments strengthening rhythmic vagal safety signals and rebuilding the cholinergic anti-inflammatory pathway, and amplification of gains through multimodal therapies—including speech, applied behavioral analysis, occupational therapy, and treatments for co-occurring conditions.
Prevention and Intervention Framework
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.
California data demonstrate proof-of-principle: ASD prevalence has peaked and started declining in subpopulations with best access to comprehensive medical care and early interventions, while prevalence continued rising through 2020 in Black children without such access living in the same counties.
The model integrates seven existing ASD frameworks: genetic, neurodevelopmental excitatory-inhibitory imbalance, gene-environment interaction, neuroinflammation and immune dysregulation, microbiome-gut-brain axis, mitochondrial dysfunction, and synaptic dysfunction models.
"eATP signaling and the CDR are common features that connect each of these modern models," Dr. Naviaux concluded.
Dr. Naviaux acknowledged that suramin—the first antipurinergic drug tested in small ASD trials—remains unauthorized outside clinical trials. "Suramin has not yet been tested in phase III clinical trials in children with ASD and is not approved for any use in the United States," Dr. Naviaux stated. "Improper use of suramin can cause harm," he concluded.
Disclosures can be found in the review.
Source: Mitochondrion