{
  "id": "44",
  "title": "Intrinsic limits on axon regrowth",
  "summary": "Growth restraint within surviving neurons may prevent adequate terminal replacement in established DPN.",
  "source_title": "Intrinsic growth restraint prevents adequate terminal replacement",
  "page": "44_intrinsic_growth_restriction.html",
  "source_markdown": "sources/44_intrinsic_growth_restriction.md",
  "structured_data": "data/44_intrinsic_growth_restriction.json",
  "snapshot_date": "2026-09-14",
  "source_review_date": "2026-09-13",
  "scope_label": "Repair in established DPN",
  "scope_exception": true,
  "source_headline_markdown": "**Base judgment: 19.0%; skeptical–optimistic sensitivity: 1.6%–55.3%.** Subjective probabilities of the causal proposition below, not effect sizes. Decimal places only show arithmetic. Reviewed 13 September 2026. [Probability method](probability_method.md) · [Collection index](README.md).",
  "probability_percent": {
    "skeptical": 1.575,
    "base": 19.0125,
    "favorable": 55.27125
  },
  "probability_meaning": "Subjective belief in the complete causal proposition. Scenario endpoints are sensitivity products, not confidence limits.",
  "causal_proposition_markdown": "In established diabetic neuropathy, neuronal growth restraint prevents adequate replacement of lost peptidergic terminals, and relieving that restraint would materially reduce continuing net denervation.\n\n**Scope:** Repair/progression exception: adults with established type 2 DPN and surviving parent neurons. Materiality means at least 20% less five-year net terminal loss in a describable subgroup comprising at least 10% of this established-DPN population. Prevention before onset remains a further extrapolation.\n\n**Causal role:** failure of replacement rather than necessarily increased destruction. Unless the scope specifies an exception, materiality means at least 20% less five-year net terminal loss in an identifiable subgroup representing at least 10% of incident DPN cases in the stated population. The target remains human peptidergic C-fibers when a study measures a broader endpoint.",
  "claims": [
    {
      "id": "R1",
      "source_id": "1",
      "claim": "Surviving neurons retain growth potential, but intrinsic restraint prevents adequate replacement relative to diabetic loss.",
      "claim_markdown": "Surviving neurons retain growth potential, but intrinsic restraint prevents adequate replacement relative to diabetic loss.",
      "conditional_percent": {
        "skeptical": 50.0,
        "base": 75.0,
        "favorable": 90.0
      },
      "cumulative_base_percent": 75.0,
      "source_cumulative_display": "75.0%",
      "reason_markdown": "Human structural treatment data support some retained capacity; net shortage alone does not identify the brake.",
      "question": "Do surviving neurons retain growth potential while intrinsic restraint prevents enough replacement to keep pace with diabetic terminal loss?"
    },
    {
      "id": "R2",
      "source_id": "2",
      "claim": "The consequential restraint is within the neuron rather than wholly an extrinsic skin, glial, vascular or fuel limitation.",
      "claim_markdown": "The consequential restraint is within the neuron rather than wholly an extrinsic skin, glial, vascular or fuel limitation.",
      "conditional_percent": {
        "skeptical": 30.0,
        "base": 60.0,
        "favorable": 85.0
      },
      "cumulative_base_percent": 45.0,
      "source_cumulative_display": "45.0%",
      "reason_markdown": "Animal neuronal manipulations support cell autonomy; topical human treatment does not identify its cellular site.",
      "question": "Is the consequential growth restraint inside the neuron, rather than entirely due to skin, glial, vascular, or fuel limitations?"
    },
    {
      "id": "R3",
      "source_id": "3",
      "claim": "Relieving the restraint generates sufficiently stable terminals, rather than only transient sprouts or marker changes.",
      "claim_markdown": "Relieving the restraint generates sufficiently stable terminals, rather than only transient sprouts or marker changes.",
      "conditional_percent": {
        "skeptical": 35.0,
        "base": 65.0,
        "favorable": 85.0
      },
      "cumulative_base_percent": 29.25,
      "source_cumulative_display": "29.3%",
      "reason_markdown": "A structural count at one follow-up is stronger than neurite outgrowth but does not establish durability or normal function.",
      "question": "Would relieving neuronal growth restraint produce stable terminals, beyond transient sprouts or marker changes?"
    },
    {
      "id": "R4",
      "source_id": "4",
      "claim": "This additional replacement would materially reduce continuing net denervation in the stated human population.",
      "claim_markdown": "This additional replacement would materially reduce continuing net denervation in the stated human population.",
      "conditional_percent": {
        "skeptical": 30.0,
        "base": 65.0,
        "favorable": 85.0
      },
      "cumulative_base_percent": 19.0125,
      "source_cumulative_display": "19.0%",
      "reason_markdown": "Ongoing destruction may erase growth; effect size, persistence and relevant subtype remain uncertain.",
      "question": "Would the additional replacement avert at least 20% of five-year net terminal loss in a subgroup comprising at least 10% of adults with established type 2 DPN?"
    }
  ],
  "sections": [
    {
      "heading": "The causal claim and its scope",
      "markdown": "In established diabetic neuropathy, neuronal growth restraint prevents adequate replacement of lost peptidergic terminals, and relieving that restraint would materially reduce continuing net denervation.\n\n**Scope:** Repair/progression exception: adults with established type 2 DPN and surviving parent neurons. Materiality means at least 20% less five-year net terminal loss in a describable subgroup comprising at least 10% of this established-DPN population. Prevention before onset remains a further extrapolation.\n\n**Causal role:** failure of replacement rather than necessarily increased destruction. Unless the scope specifies an exception, materiality means at least 20% less five-year net terminal loss in an identifiable subgroup representing at least 10% of incident DPN cases in the stated population. The target remains human peptidergic C-fibers when a study measures a broader endpoint."
    },
    {
      "heading": "Reasoning from the biological requirements",
      "markdown": "Terminal abundance changes by additions minus losses. Even an ordinary rate of terminal damage produces progressive denervation if replacement cannot keep up. A growth brake need not be abnormally expressed: a normal restraint can become consequential when replacement demand rises. However, pharmacologically forcing growth does not show that an intrinsic brake was the natural bottleneck. New branches must persist and become useful terminals; brief sprouting or altered staining is insufficient. M1 muscarinic and PTEN-related signaling are candidate branches, not jointly necessary links."
    },
    {
      "heading": "Probabilities of the necessary claims",
      "markdown": "Conditional prices are skeptical / base / optimistic. Each price after the first assumes *all earlier requirements are true*. Their order is an order for assessing joint belief, not necessarily a linear biological pathway. The cumulative column uses the base scenario. Temporal order, connected compartments and the causal prevention comparison are included in these requirements, without extra generic multipliers.\n\n| # | Necessary claim | Conditional YES | Cumulative YES | Reason for this judgment |\n|---|---|---:|---:|---|\n| 1 | Surviving neurons retain growth potential, but intrinsic restraint prevents adequate replacement relative to diabetic loss. | 50 / **75** / 90% | 75.0% | Human structural treatment data support some retained capacity; net shortage alone does not identify the brake. |\n| 2 | The consequential restraint is within the neuron rather than wholly an extrinsic skin, glial, vascular or fuel limitation. | 30 / **60** / 85% | 45.0% | Animal neuronal manipulations support cell autonomy; topical human treatment does not identify its cellular site. |\n| 3 | Relieving the restraint generates sufficiently stable terminals, rather than only transient sprouts or marker changes. | 35 / **65** / 85% | 29.3% | A structural count at one follow-up is stronger than neurite outgrowth but does not establish durability or normal function. |\n| 4 | This additional replacement would materially reduce continuing net denervation in the stated human population. | 30 / **65** / 85% | 19.0% | Ongoing destruction may erase growth; effect size, persistence and relevant subtype remain uncertain. |"
    },
    {
      "heading": "Evidence that moves the judgment",
      "markdown": "- Selective M1 antagonism and genetic manipulation increased sensory-neuron outgrowth and protected peripheral nerve indices in experimental neuropathies, with mitochondrial/AMPK-related effects. The findings support a neuronal growth-control route but do not prove pathological M1 overactivity in human diabetes. [Calcutt et al., 2017](https://www.jci.org/articles/view/88321).\n\n- The newer pirenzepine study randomized 58 people with established type 2 DPN; 57 entered modified intention-to-treat analysis. At 24 weeks, treated-ankle IENFD changed by +1.8 fibers/mm in pooled treatment versus −0.6 with placebo, with baseline-adjusted between-group P=.012. Other efficacy outcomes did not differ in that analysis. This is a human structural signal, without exact peptidergic identification, cellular localization or five-year persistence. [Sivadasan et al., published online 2025](https://pmc.ncbi.nlm.nih.gov/articles/PMC12721300/).\n\n- The oxybutynin trial randomized 51 participants and reported within-arm IENFD improvement. The repository's reconstruction of 37 readable primary biopsy pairs gives a treatment-minus-placebo change of +0.833 fibers/mm, 95% CI −0.723 to +2.390, P=.282; a secondary sprouting contrast remains provisional. A significant change in one arm does not establish superiority. [Primary paper](https://doi.org/10.1007/s00401-024-02710-4); [public-figure reanalysis](../../../findings/idea46_oxybutynin_randomized_reanalysis.md).\n\n- Combined PTEN knockdown and local insulin promoted repair in a diabetic experimental setting, but a combined intervention cannot identify which natural deficit was limiting. [2023 primary study](https://diabetesjournals.org/diabetes/article/72/6/795/148608/Combined-PTEN-Knockdown-and-Local-Insulin-in)."
    },
    {
      "heading": "Why these odds and how uncertain they are",
      "markdown": "The pirenzepine randomized structural contrast makes retained human repair capacity considerably more credible than culture outgrowth alone. I do not price the full causal hypothesis nearly as highly, because the positive trial neither identifies the cellular site nor demonstrates that a growth brake caused the original loss. The principal uncertain link is neuronal localization. A broad proposition that local treatment can increase some epidermal fibers is easier than this specific intrinsic, durable, peptidergic mechanism.\n\nThe skeptical scenario puts the treatment effect in skin/support cells or short-lived growth that does not offset continuing injury. The optimistic scenario interprets the human structural signal as lifting a neuronal maintenance restraint with durable replacement. Programme-internal convergence is not independent replication; the repository's later [replication search](../../../findings/grad52_pirenzepine_replication_no_go.md) found no publicly reported efficacy contrast from the separate completed trial. The [dynamic-trial analysis](../../../findings/f8_dynamic_trial_model_gates.md) also could not identify sprout maturation or treatment compartment from the public observations.\n\nConditional inputs: base **[75, 60, 65, 65]%**; skeptical **[50, 30, 35, 30]%**; optimistic **[90, 85, 85, 85]%**. Products give the headline prices. The span measures sensitivity to these interpretations; it is not a statistical confidence interval.\n\n**Numerical update example:** Public human data separating a neuronal target effect from skin/glial exposure would raise requirement 2; credible localization entirely to extrinsic support would lower this intrinsic claim while potentially raising hypothesis 32. Changing only requirement 2 from 60% to 85% raises the whole price to **26.9%**; reducing it to 20% lowers the price to **6.3%**. These are hypothetical evidence updates. Even resolving that one requirement with certainty would leave a complete price of 31.7% if the others stayed unchanged."
    },
    {
      "heading": "Overlap and boundary",
      "markdown": "Complements the extrinsic [skin repair environment](32_skin_repair_environment.md) and [trophic support](14_ngf_trophic_support.md) hypotheses. [Energy](07_bioenergetic_insufficiency.md) and [transport](26_axonal_transport.md) can constrain the growth response. The probability of this causal account is different from the probability that pirenzepine has some treatment benefit."
    }
  ],
  "source_claim_table_markdown": "| # | Necessary claim | Conditional YES | Cumulative YES | Reason for this judgment |\n|---|---|---:|---:|---|\n| 1 | Surviving neurons retain growth potential, but intrinsic restraint prevents adequate replacement relative to diabetic loss. | 50 / **75** / 90% | 75.0% | Human structural treatment data support some retained capacity; net shortage alone does not identify the brake. |\n| 2 | The consequential restraint is within the neuron rather than wholly an extrinsic skin, glial, vascular or fuel limitation. | 30 / **60** / 85% | 45.0% | Animal neuronal manipulations support cell autonomy; topical human treatment does not identify its cellular site. |\n| 3 | Relieving the restraint generates sufficiently stable terminals, rather than only transient sprouts or marker changes. | 35 / **65** / 85% | 29.3% | A structural count at one follow-up is stronger than neurite outgrowth but does not establish durability or normal function. |\n| 4 | This additional replacement would materially reduce continuing net denervation in the stated human population. | 30 / **65** / 85% | 19.0% | Ongoing destruction may erase growth; effect size, persistence and relevant subtype remain uncertain. |"
}