The Sodium Struggle Hypothesis: Autism as a Manifestation of Compensatory Physiology in Coupled Osmotic–Volume Defence

The Sodium Struggle Hypothesis: Autism as a Manifestation of Compensatory Physiology in Coupled Osmotic–Volume Defence (previously: The Sodium Struggle: Autism as a Manifestation of Compensatory Measures Against Hyponatraemia and Hypovolaemia) author: Kathleen Roberta Bell Summary of the hypothesis and evidence-synthesis manuscript, revised 1 November 2026. The Sodium Struggle Hypothesis proposes that diverse initiating conditions can contribute to later features of autism through impaired local neural or glial ionic or cell-volume recovery during sensitive development. Systemic routes alter tonicity, effective filling, tissue delivery or their regulation. Intrinsic routes begin with constraints on cellular transport, energetic support or restoration. Recovery must be slower, less complete or less stable than in an appropriate comparator, and that disturbance must change a defined developmental process. Participation across all autistic trajectories remains an unestablished conjecture. Renal, vascular, endocrine, autonomic and cellular responses can preserve immediate function and prevent lasting impairment. Developmental cost requires constrained recovery during a defined process, not protective recruitment or energy expenditure alone. An early disturbance could alter circuit construction and resolve, leaving consequences without continuing swelling, abnormal blood chemistry or a hormonal signature. Initiation, compensation, recovery, developmental conversion, persistence and later expression are overlapping explanatory roles, not compulsory stages. Sodium concentration, total sodium, tonicity, circulating volume and regional perfusion are distinct. Normal serum sodium neither establishes adequate local recovery nor proves hidden dysfunction. “Low-effective-sodium pressure” is a heuristic for specified solute, water, filling, delivery and regulatory relationships, not an analyte or alternative diagnosis. Clinical hyponatraemia retains its usual meaning. Hyponatraemia, hypo-osmolality and hypovolaemia remain important working examples. Hypertonic exposure, genuine volume expansion and direct cellular constraints need not involve an impending low state. Actual underfilling, impaired effective filling despite fluid expansion, and circulatory sensing errors require separate descriptions. Vasopressin (AVP), the renin–angiotensin–aldosterone system (RAAS), glucocorticoid support, autonomic responses and renal sodium–water handling provide complementary regulatory arms. They need not rise together. Hypotonicity can suppress osmotic AVP recruitment, whereas hypertonicity or circulatory threat can stimulate it through different inputs. Secretion, clearance, receptor responsiveness and downstream function determine the effect. “Wet” and “dry” describe continuous, potentially mixed or changing weightings of water conservation and vascular support, not fixed autistic subtypes. Genetic initiation is integral. Altered transport, cytoskeletal organisation or metabolic support could constrain recovery without maternal exposure or systemic sodium deficit; other variants could increase demand on intact machinery. The genetic tables distinguish demand and defence execution from local regulation and reserve without a primary–secondary hierarchy. Variant, dosage, tissue, stage and direction delimit each claim. The frozen Satterstrom-102 count of 42/102 qualifying components is not a count of demonstrated recovery defects, statistical enrichment or recovery-mediated developmental effects. Maternal and placental routes include disturbed water–solute balance, metabolic or immune conditions, medication-related fluid effects and vascular or renal constraints. Each requires evidence of fetal exposure and response. Low-mineral water does not establish dilution; retained water, solute and excretion determine the state. Maternal salt intake establishes neither fetal hypertonicity nor AVP-mediated rebound. Hypertonic exposure, hypotonic overshoot and delayed withdrawal of water conservation or cellular adaptations are distinct candidate trajectories. The placenta transforms maternal conditions through transport, metabolism and vascular regulation. Water or glucose changes need not entail maternal AVP transfer. Placental vasopressinase activity involves insulin-regulated aminopeptidase (IRAP); circulating and tissue-associated forms differ, and cortisol metabolism is separate. Pregnancy clearance and fetal pituitary detection findings establish neither the onset of functional fetal AVP regulation nor an AVP-defined autism susceptibility window. Timing is mechanism-specific. Maternal immune activation can act through transferred molecules, placental or fetal mediators, or altered vascular function and delivery. Severe challenge has produced placental congestion and abnormal fetal haemodynamics in mice; other preparations show maintained estimated cerebral oxygen delivery or injury without detected Doppler changes. Hypoperfusion is not inevitable. The vascular route must connect fetal delivery, energetic state and local recovery; maternal concentrations cannot substitute for fetal exposure. Immune mechanisms can act locally: experiments show altered neuronal chloride regulation and GABA maturation, while IL-17A produces developmental effects in human fetal cerebroids without systemic circulation. These demonstrate susceptibility or ionic disruption, not recovery-mediated development. Maternal brain-reactive IgG is a distinct exposure requiring antibody specificity and fetal target access. Direct immune developmental effects remain possible routes around the recovery intermediary. Glucose–insulin physiology supplies two independent proposals. Extracellular glucose can increase effective tonicity and draw water out of cells, lowering measured sodium through redistribution rather than hypotonic dilution. Temporary glucose mobilisation or reduced disposal is proposed as possible immediate osmotic support. Separately, insulin-associated IRAP trafficking and peripheral AVP processing could modify peptide exposure and water handling without a preceding protective glucose rise. Trafficking, accessible enzyme activity and native-peptide clearance are different measurements. Impaired glucose disposal does not establish impaired AVP clearance. Coordination, glutathione-sensitive processing and inflammatory feedback remain conditional questions. Phosphate's direct osmotic contribution differs from its endocrine and renal effects. Phosphate disposal can interact with sodium conservation, but phosphaturia does not establish net sodium loss. PTH, FGF23, renin and aldosterone require exposure-specific interpretation. The proposed “osmotic pendulum” requires measured recurrent excursions and causal feedback among mineral, sodium, water and vascular responses. Asynchronous hormone peaks do not establish oscillation; stable recovery remains possible. NKCC1-mediated influx can increase intracellular sodium and chloride and ATP-dependent sodium extrusion. Impaired KCC2 chloride extrusion is a different constraint, not proof of greater NKCC1 influx or sodium loading. Pump turnover can increase with maintained ATP and adequate recovery. Calcium entry, sodium–calcium exchange and oxidative signalling depend on gradients, cell type and physiological state. Intracellular ATP availability, turnover and extracellular ATP signalling remain distinct. Regulatory volume decrease during maintained hypotonic exposure differs from restoration after extracellular conditions normalise and replenishment of lost organic osmolytes. A cell can regain volume while ionic composition or osmolyte reserve remains altered. The proposed “osmolyte debt” concerns measured loss or inadequate replenishment that makes subsequent challenges harder to resolve. Severe disturbances demonstrate different ionic and organic-osmolyte recovery times; persistence after mild, repeated developmental challenges remains unestablished. Challenge spacing is therefore a testable variable beyond peak magnitude, number or cumulative exposure. Local recovery could affect inhibitory maturation, synaptic refinement, extracellular-matrix assembly or myelination. Depolarising GABA does not necessarily abolish inhibition. Astrocytic buffering, extracellular space, choroid-plexus secretion and OTX2 transport provide further interfaces. Cerebrospinal-fluid (CSF) volume does not measure clearance, and protein abundance does not establish secretion or uptake. Delayed, accelerated and unchanged findings constrain universal immaturity; predictions require a specified process and interval. Redox-dependent loss of nitric-oxide signalling could impair delivery or circulatory sensing; successful compensation could interrupt that route. Hypoxia and substrate deprivation can disturb ionic regulation without systemic sodium–volume abnormality. If matched oxygen or substrate exposure explains an effect without a measurable osmotic–volume contribution, that systemic branch loses support. Whether local recovery mediates the metabolic effect remains a separate question. Membrane and matrix protection need not accelerate restoration: cholesterol depletion improved volume recovery in a retained cell-model finding. Circulating cholesterol does not measure neuronal membrane sterol supply. Direct developmental effects of sterols or extracellular signalling remain alternatives until their relationship to recovery is measured. Renal, adrenal, vascular and receptor mechanisms can modify recovery demands. Nephron endowment, functional reserve and kidney injury are distinct; renal involvement may be upstream, downstream or parallel to neural effects. Adrenal interpretation requires species, stage and functional response. Persistent hormone action may reflect continuing exposure, clearance, receptors or controll